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1374 lines
58 KiB
1374 lines
58 KiB
<h1><img src="https://terser.org/img/terser-banner-logo.png" alt="Terser" width="400"></h1> |
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[![NPM Version][npm-image]][npm-url] |
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[![NPM Downloads][downloads-image]][downloads-url] |
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[![Travis Build][travis-image]][travis-url] |
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[![Opencollective financial contributors][opencollective-contributors]][opencollective-url] |
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A JavaScript mangler/compressor toolkit for ES6+. |
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*note*: You can support this project on patreon: <a target="_blank" rel="nofollow" href="https://www.patreon.com/fabiosantoscode"><img src="https://c5.patreon.com/external/logo/become_a_patron_button@2x.png" alt="patron" width="100px" height="auto"></a>. Check out [PATRONS.md](https://github.com/terser/terser/blob/master/PATRONS.md) for our first-tier patrons. |
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Terser recommends you use RollupJS to bundle your modules, as that produces smaller code overall. |
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*Beautification* has been undocumented and is *being removed* from terser, we recommend you use [prettier](https://npmjs.com/package/prettier). |
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Find the changelog in [CHANGELOG.md](https://github.com/terser/terser/blob/master/CHANGELOG.md) |
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[npm-image]: https://img.shields.io/npm/v/terser.svg |
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[npm-url]: https://npmjs.org/package/terser |
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[downloads-image]: https://img.shields.io/npm/dm/terser.svg |
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[downloads-url]: https://npmjs.org/package/terser |
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[travis-image]: https://app.travis-ci.com/terser/terser.svg?branch=master |
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[travis-url]: https://app.travis-ci.com/github/terser/terser |
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[opencollective-contributors]: https://opencollective.com/terser/tiers/badge.svg |
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[opencollective-url]: https://opencollective.com/terser |
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Why choose terser? |
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------------------ |
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`uglify-es` is [no longer maintained](https://github.com/mishoo/UglifyJS2/issues/3156#issuecomment-392943058) and `uglify-js` does not support ES6+. |
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**`terser`** is a fork of `uglify-es` that mostly retains API and CLI compatibility |
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with `uglify-es` and `uglify-js@3`. |
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Install |
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------- |
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First make sure you have installed the latest version of [node.js](http://nodejs.org/) |
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(You may need to restart your computer after this step). |
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From NPM for use as a command line app: |
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npm install terser -g |
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From NPM for programmatic use: |
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npm install terser |
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# Command line usage |
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<!-- CLI_USAGE:START --> |
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terser [input files] [options] |
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Terser can take multiple input files. It's recommended that you pass the |
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input files first, then pass the options. Terser will parse input files |
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in sequence and apply any compression options. The files are parsed in the |
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same global scope, that is, a reference from a file to some |
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variable/function declared in another file will be matched properly. |
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Command line arguments that take options (like --parse, --compress, --mangle and |
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--format) can take in a comma-separated list of default option overrides. For |
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instance: |
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terser input.js --compress ecma=2015,computed_props=false |
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If no input file is specified, Terser will read from STDIN. |
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If you wish to pass your options before the input files, separate the two with |
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a double dash to prevent input files being used as option arguments: |
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terser --compress --mangle -- input.js |
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### Command line options |
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``` |
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-h, --help Print usage information. |
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`--help options` for details on available options. |
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-V, --version Print version number. |
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-p, --parse <options> Specify parser options: |
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`acorn` Use Acorn for parsing. |
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`bare_returns` Allow return outside of functions. |
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Useful when minifying CommonJS |
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modules and Userscripts that may |
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be anonymous function wrapped (IIFE) |
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by the .user.js engine `caller`. |
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`expression` Parse a single expression, rather than |
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a program (for parsing JSON). |
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`spidermonkey` Assume input files are SpiderMonkey |
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AST format (as JSON). |
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-c, --compress [options] Enable compressor/specify compressor options: |
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`pure_funcs` List of functions that can be safely |
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removed when their return values are |
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not used. |
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-m, --mangle [options] Mangle names/specify mangler options: |
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`reserved` List of names that should not be mangled. |
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--mangle-props [options] Mangle properties/specify mangler options: |
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`builtins` Mangle property names that overlaps |
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with standard JavaScript globals and DOM |
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API props. |
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`debug` Add debug prefix and suffix. |
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`keep_quoted` Only mangle unquoted properties, quoted |
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properties are automatically reserved. |
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`strict` disables quoted properties |
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being automatically reserved. |
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`regex` Only mangle matched property names. |
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`reserved` List of names that should not be mangled. |
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-f, --format [options] Specify format options. |
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`preamble` Preamble to prepend to the output. You |
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can use this to insert a comment, for |
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example for licensing information. |
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This will not be parsed, but the source |
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map will adjust for its presence. |
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`quote_style` Quote style: |
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0 - auto |
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1 - single |
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2 - double |
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3 - original |
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`wrap_iife` Wrap IIFEs in parenthesis. Note: you may |
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want to disable `negate_iife` under |
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compressor options. |
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`wrap_func_args` Wrap function arguments in parenthesis. |
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-o, --output <file> Output file path (default STDOUT). Specify `ast` or |
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`spidermonkey` to write Terser or SpiderMonkey AST |
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as JSON to STDOUT respectively. |
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--comments [filter] Preserve copyright comments in the output. By |
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default this works like Google Closure, keeping |
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JSDoc-style comments that contain e.g. "@license", |
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or start with "!". You can optionally pass one of the |
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following arguments to this flag: |
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- "all" to keep all comments |
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- `false` to omit comments in the output |
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- a valid JS RegExp like `/foo/` or `/^!/` to |
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keep only matching comments. |
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Note that currently not *all* comments can be |
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kept when compression is on, because of dead |
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code removal or cascading statements into |
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sequences. |
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--config-file <file> Read `minify()` options from JSON file. |
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-d, --define <expr>[=value] Global definitions. |
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--ecma <version> Specify ECMAScript release: 5, 2015, 2016, etc. |
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-e, --enclose [arg[:value]] Embed output in a big function with configurable |
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arguments and values. |
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--ie8 Support non-standard Internet Explorer 8. |
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Equivalent to setting `ie8: true` in `minify()` |
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for `compress`, `mangle` and `format` options. |
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By default Terser will not try to be IE-proof. |
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--keep-classnames Do not mangle/drop class names. |
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--keep-fnames Do not mangle/drop function names. Useful for |
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code relying on Function.prototype.name. |
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--module Input is an ES6 module. If `compress` or `mangle` is |
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enabled then the `toplevel` option will be enabled. |
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--name-cache <file> File to hold mangled name mappings. |
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--safari10 Support non-standard Safari 10/11. |
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Equivalent to setting `safari10: true` in `minify()` |
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for `mangle` and `format` options. |
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By default `terser` will not work around |
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Safari 10/11 bugs. |
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--source-map [options] Enable source map/specify source map options: |
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`base` Path to compute relative paths from input files. |
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`content` Input source map, useful if you're compressing |
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JS that was generated from some other original |
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code. Specify "inline" if the source map is |
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included within the sources. |
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`filename` Name and/or location of the output source. |
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`includeSources` Pass this flag if you want to include |
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the content of source files in the |
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source map as sourcesContent property. |
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`root` Path to the original source to be included in |
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the source map. |
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`url` If specified, path to the source map to append in |
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`//# sourceMappingURL`. |
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--timings Display operations run time on STDERR. |
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--toplevel Compress and/or mangle variables in top level scope. |
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--wrap <name> Embed everything in a big function, making the |
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“exports” and “global” variables available. You |
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need to pass an argument to this option to |
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specify the name that your module will take |
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when included in, say, a browser. |
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``` |
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Specify `--output` (`-o`) to declare the output file. Otherwise the output |
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goes to STDOUT. |
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## CLI source map options |
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Terser can generate a source map file, which is highly useful for |
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debugging your compressed JavaScript. To get a source map, pass |
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`--source-map --output output.js` (source map will be written out to |
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`output.js.map`). |
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Additional options: |
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- `--source-map "filename='<NAME>'"` to specify the name of the source map. |
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- `--source-map "root='<URL>'"` to pass the URL where the original files can be found. |
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- `--source-map "url='<URL>'"` to specify the URL where the source map can be found. |
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Otherwise Terser assumes HTTP `X-SourceMap` is being used and will omit the |
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`//# sourceMappingURL=` directive. |
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For example: |
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terser js/file1.js js/file2.js \ |
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-o foo.min.js -c -m \ |
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--source-map "root='http://foo.com/src',url='foo.min.js.map'" |
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The above will compress and mangle `file1.js` and `file2.js`, will drop the |
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output in `foo.min.js` and the source map in `foo.min.js.map`. The source |
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mapping will refer to `http://foo.com/src/js/file1.js` and |
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`http://foo.com/src/js/file2.js` (in fact it will list `http://foo.com/src` |
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as the source map root, and the original files as `js/file1.js` and |
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`js/file2.js`). |
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### Composed source map |
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When you're compressing JS code that was output by a compiler such as |
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CoffeeScript, mapping to the JS code won't be too helpful. Instead, you'd |
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like to map back to the original code (i.e. CoffeeScript). Terser has an |
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option to take an input source map. Assuming you have a mapping from |
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CoffeeScript → compiled JS, Terser can generate a map from CoffeeScript → |
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compressed JS by mapping every token in the compiled JS to its original |
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location. |
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To use this feature pass `--source-map "content='/path/to/input/source.map'"` |
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or `--source-map "content=inline"` if the source map is included inline with |
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the sources. |
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## CLI compress options |
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You need to pass `--compress` (`-c`) to enable the compressor. Optionally |
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you can pass a comma-separated list of [compress options](#compress-options). |
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Options are in the form `foo=bar`, or just `foo` (the latter implies |
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a boolean option that you want to set `true`; it's effectively a |
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shortcut for `foo=true`). |
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Example: |
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terser file.js -c toplevel,sequences=false |
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## CLI mangle options |
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To enable the mangler you need to pass `--mangle` (`-m`). The following |
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(comma-separated) options are supported: |
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- `toplevel` (default `false`) -- mangle names declared in the top level scope. |
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- `eval` (default `false`) -- mangle names visible in scopes where `eval` or `with` are used. |
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When mangling is enabled but you want to prevent certain names from being |
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mangled, you can declare those names with `--mangle reserved` — pass a |
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comma-separated list of names. For example: |
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terser ... -m reserved=['$','require','exports'] |
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to prevent the `require`, `exports` and `$` names from being changed. |
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### CLI mangling property names (`--mangle-props`) |
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**Note:** THIS **WILL** BREAK YOUR CODE. A good rule of thumb is not to use this unless you know exactly what you're doing and how this works and read this section until the end. |
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Mangling property names is a separate step, different from variable name mangling. Pass |
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`--mangle-props` to enable it. The least dangerous |
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way to use this is to use the `regex` option like so: |
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``` |
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terser example.js -c -m --mangle-props regex=/_$/ |
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``` |
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This will mangle all properties that end with an |
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underscore. So you can use it to mangle internal methods. |
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By default, it will mangle all properties in the |
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input code with the exception of built in DOM properties and properties |
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in core JavaScript classes, which is what will break your code if you don't: |
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1. Control all the code you're mangling |
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2. Avoid using a module bundler, as they usually will call Terser on each file individually, making it impossible to pass mangled objects between modules. |
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3. Avoid calling functions like `defineProperty` or `hasOwnProperty`, because they refer to object properties using strings and will break your code if you don't know what you are doing. |
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An example: |
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```javascript |
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// example.js |
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var x = { |
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baz_: 0, |
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foo_: 1, |
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calc: function() { |
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return this.foo_ + this.baz_; |
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} |
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}; |
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x.bar_ = 2; |
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x["baz_"] = 3; |
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console.log(x.calc()); |
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``` |
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Mangle all properties (except for JavaScript `builtins`) (**very** unsafe): |
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```bash |
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$ terser example.js -c passes=2 -m --mangle-props |
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``` |
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```javascript |
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var x={o:3,t:1,i:function(){return this.t+this.o},s:2};console.log(x.i()); |
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``` |
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Mangle all properties except for `reserved` properties (still very unsafe): |
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```bash |
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$ terser example.js -c passes=2 -m --mangle-props reserved=[foo_,bar_] |
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``` |
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```javascript |
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var x={o:3,foo_:1,t:function(){return this.foo_+this.o},bar_:2};console.log(x.t()); |
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``` |
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Mangle all properties matching a `regex` (not as unsafe but still unsafe): |
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```bash |
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$ terser example.js -c passes=2 -m --mangle-props regex=/_$/ |
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``` |
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```javascript |
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var x={o:3,t:1,calc:function(){return this.t+this.o},i:2};console.log(x.calc()); |
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``` |
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Combining mangle properties options: |
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```bash |
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$ terser example.js -c passes=2 -m --mangle-props regex=/_$/,reserved=[bar_] |
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``` |
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```javascript |
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var x={o:3,t:1,calc:function(){return this.t+this.o},bar_:2};console.log(x.calc()); |
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``` |
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In order for this to be of any use, we avoid mangling standard JS names and DOM |
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API properties by default (`--mangle-props builtins` to override). |
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A regular expression can be used to define which property names should be |
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mangled. For example, `--mangle-props regex=/^_/` will only mangle property |
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names that start with an underscore. |
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When you compress multiple files using this option, in order for them to |
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work together in the end we need to ensure somehow that one property gets |
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mangled to the same name in all of them. For this, pass `--name-cache filename.json` |
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and Terser will maintain these mappings in a file which can then be reused. |
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It should be initially empty. Example: |
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```bash |
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$ rm -f /tmp/cache.json # start fresh |
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$ terser file1.js file2.js --mangle-props --name-cache /tmp/cache.json -o part1.js |
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$ terser file3.js file4.js --mangle-props --name-cache /tmp/cache.json -o part2.js |
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``` |
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Now, `part1.js` and `part2.js` will be consistent with each other in terms |
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of mangled property names. |
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Using the name cache is not necessary if you compress all your files in a |
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single call to Terser. |
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### Mangling unquoted names (`--mangle-props keep_quoted`) |
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Using quoted property name (`o["foo"]`) reserves the property name (`foo`) |
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so that it is not mangled throughout the entire script even when used in an |
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unquoted style (`o.foo`). Example: |
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```javascript |
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// stuff.js |
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var o = { |
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"foo": 1, |
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bar: 3 |
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}; |
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o.foo += o.bar; |
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console.log(o.foo); |
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``` |
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```bash |
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$ terser stuff.js --mangle-props keep_quoted -c -m |
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``` |
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```javascript |
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var o={foo:1,o:3};o.foo+=o.o,console.log(o.foo); |
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``` |
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### Debugging property name mangling |
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You can also pass `--mangle-props debug` in order to mangle property names |
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without completely obscuring them. For example the property `o.foo` |
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would mangle to `o._$foo$_` with this option. This allows property mangling |
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of a large codebase while still being able to debug the code and identify |
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where mangling is breaking things. |
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```bash |
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$ terser stuff.js --mangle-props debug -c -m |
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``` |
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```javascript |
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var o={_$foo$_:1,_$bar$_:3};o._$foo$_+=o._$bar$_,console.log(o._$foo$_); |
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``` |
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You can also pass a custom suffix using `--mangle-props debug=XYZ`. This would then |
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mangle `o.foo` to `o._$foo$XYZ_`. You can change this each time you compile a |
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script to identify how a property got mangled. One technique is to pass a |
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random number on every compile to simulate mangling changing with different |
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inputs (e.g. as you update the input script with new properties), and to help |
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identify mistakes like writing mangled keys to storage. |
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<!-- CLI_USAGE:END --> |
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# API Reference |
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<!-- API_REFERENCE:START --> |
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Assuming installation via NPM, you can load Terser in your application |
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like this: |
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```javascript |
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const { minify } = require("terser"); |
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``` |
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Or, |
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```javascript |
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import { minify } from "terser"; |
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``` |
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Browser loading is also supported: |
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```html |
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<script src="https://cdn.jsdelivr.net/npm/source-map@0.7.3/dist/source-map.js"></script> |
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<script src="https://cdn.jsdelivr.net/npm/terser/dist/bundle.min.js"></script> |
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``` |
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There is a single async high level function, **`async minify(code, options)`**, |
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which will perform all minification [phases](#minify-options) in a configurable |
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manner. By default `minify()` will enable [`compress`](#compress-options) |
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and [`mangle`](#mangle-options). Example: |
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```javascript |
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var code = "function add(first, second) { return first + second; }"; |
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var result = await minify(code, { sourceMap: true }); |
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console.log(result.code); // minified output: function add(n,d){return n+d} |
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console.log(result.map); // source map |
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``` |
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You can `minify` more than one JavaScript file at a time by using an object |
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for the first argument where the keys are file names and the values are source |
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code: |
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```javascript |
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var code = { |
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"file1.js": "function add(first, second) { return first + second; }", |
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"file2.js": "console.log(add(1 + 2, 3 + 4));" |
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}; |
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var result = await minify(code); |
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console.log(result.code); |
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// function add(d,n){return d+n}console.log(add(3,7)); |
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``` |
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The `toplevel` option: |
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```javascript |
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var code = { |
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"file1.js": "function add(first, second) { return first + second; }", |
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"file2.js": "console.log(add(1 + 2, 3 + 4));" |
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}; |
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var options = { toplevel: true }; |
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var result = await minify(code, options); |
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console.log(result.code); |
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// console.log(3+7); |
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``` |
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The `nameCache` option: |
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```javascript |
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var options = { |
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mangle: { |
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toplevel: true, |
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}, |
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nameCache: {} |
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}; |
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var result1 = await minify({ |
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"file1.js": "function add(first, second) { return first + second; }" |
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}, options); |
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var result2 = await minify({ |
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"file2.js": "console.log(add(1 + 2, 3 + 4));" |
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}, options); |
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console.log(result1.code); |
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// function n(n,r){return n+r} |
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console.log(result2.code); |
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// console.log(n(3,7)); |
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``` |
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You may persist the name cache to the file system in the following way: |
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```javascript |
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var cacheFileName = "/tmp/cache.json"; |
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var options = { |
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mangle: { |
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properties: true, |
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}, |
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nameCache: JSON.parse(fs.readFileSync(cacheFileName, "utf8")) |
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}; |
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fs.writeFileSync("part1.js", await minify({ |
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"file1.js": fs.readFileSync("file1.js", "utf8"), |
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"file2.js": fs.readFileSync("file2.js", "utf8") |
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}, options).code, "utf8"); |
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fs.writeFileSync("part2.js", await minify({ |
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"file3.js": fs.readFileSync("file3.js", "utf8"), |
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"file4.js": fs.readFileSync("file4.js", "utf8") |
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}, options).code, "utf8"); |
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fs.writeFileSync(cacheFileName, JSON.stringify(options.nameCache), "utf8"); |
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``` |
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An example of a combination of `minify()` options: |
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```javascript |
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var code = { |
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"file1.js": "function add(first, second) { return first + second; }", |
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"file2.js": "console.log(add(1 + 2, 3 + 4));" |
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}; |
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var options = { |
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toplevel: true, |
|
compress: { |
|
global_defs: { |
|
"@console.log": "alert" |
|
}, |
|
passes: 2 |
|
}, |
|
format: { |
|
preamble: "/* minified */" |
|
} |
|
}; |
|
var result = await minify(code, options); |
|
console.log(result.code); |
|
// /* minified */ |
|
// alert(10);" |
|
``` |
|
|
|
An error example: |
|
```javascript |
|
try { |
|
const result = await minify({"foo.js" : "if (0) else console.log(1);"}); |
|
// Do something with result |
|
} catch (error) { |
|
const { message, filename, line, col, pos } = error; |
|
// Do something with error |
|
} |
|
``` |
|
|
|
## Minify options |
|
|
|
- `ecma` (default `undefined`) - pass `5`, `2015`, `2016`, etc to override |
|
`compress` and `format`'s `ecma` options. |
|
|
|
- `enclose` (default `false`) - pass `true`, or a string in the format |
|
of `"args[:values]"`, where `args` and `values` are comma-separated |
|
argument names and values, respectively, to embed the output in a big |
|
function with the configurable arguments and values. |
|
|
|
- `parse` (default `{}`) — pass an object if you wish to specify some |
|
additional [parse options](#parse-options). |
|
|
|
- `compress` (default `{}`) — pass `false` to skip compressing entirely. |
|
Pass an object to specify custom [compress options](#compress-options). |
|
|
|
- `mangle` (default `true`) — pass `false` to skip mangling names, or pass |
|
an object to specify [mangle options](#mangle-options) (see below). |
|
|
|
- `mangle.properties` (default `false`) — a subcategory of the mangle option. |
|
Pass an object to specify custom [mangle property options](#mangle-properties-options). |
|
|
|
- `module` (default `false`) — Use when minifying an ES6 module. "use strict" |
|
is implied and names can be mangled on the top scope. If `compress` or |
|
`mangle` is enabled then the `toplevel` option will be enabled. |
|
|
|
- `format` or `output` (default `null`) — pass an object if you wish to specify |
|
additional [format options](#format-options). The defaults are optimized |
|
for best compression. |
|
|
|
- `sourceMap` (default `false`) - pass an object if you wish to specify |
|
[source map options](#source-map-options). |
|
|
|
- `toplevel` (default `false`) - set to `true` if you wish to enable top level |
|
variable and function name mangling and to drop unused variables and functions. |
|
|
|
- `nameCache` (default `null`) - pass an empty object `{}` or a previously |
|
used `nameCache` object if you wish to cache mangled variable and |
|
property names across multiple invocations of `minify()`. Note: this is |
|
a read/write property. `minify()` will read the name cache state of this |
|
object and update it during minification so that it may be |
|
reused or externally persisted by the user. |
|
|
|
- `ie8` (default `false`) - set to `true` to support IE8. |
|
|
|
- `keep_classnames` (default: `undefined`) - pass `true` to prevent discarding or mangling |
|
of class names. Pass a regular expression to only keep class names matching that regex. |
|
|
|
- `keep_fnames` (default: `false`) - pass `true` to prevent discarding or mangling |
|
of function names. Pass a regular expression to only keep function names matching that regex. |
|
Useful for code relying on `Function.prototype.name`. If the top level minify option |
|
`keep_classnames` is `undefined` it will be overridden with the value of the top level |
|
minify option `keep_fnames`. |
|
|
|
- `safari10` (default: `false`) - pass `true` to work around Safari 10/11 bugs in |
|
loop scoping and `await`. See `safari10` options in [`mangle`](#mangle-options) |
|
and [`format`](#format-options) for details. |
|
|
|
## Minify options structure |
|
|
|
```javascript |
|
{ |
|
parse: { |
|
// parse options |
|
}, |
|
compress: { |
|
// compress options |
|
}, |
|
mangle: { |
|
// mangle options |
|
|
|
properties: { |
|
// mangle property options |
|
} |
|
}, |
|
format: { |
|
// format options (can also use `output` for backwards compatibility) |
|
}, |
|
sourceMap: { |
|
// source map options |
|
}, |
|
ecma: 5, // specify one of: 5, 2015, 2016, etc. |
|
enclose: false, // or specify true, or "args:values" |
|
keep_classnames: false, |
|
keep_fnames: false, |
|
ie8: false, |
|
module: false, |
|
nameCache: null, // or specify a name cache object |
|
safari10: false, |
|
toplevel: false |
|
} |
|
``` |
|
|
|
### Source map options |
|
|
|
To generate a source map: |
|
```javascript |
|
var result = await minify({"file1.js": "var a = function() {};"}, { |
|
sourceMap: { |
|
filename: "out.js", |
|
url: "out.js.map" |
|
} |
|
}); |
|
console.log(result.code); // minified output |
|
console.log(result.map); // source map |
|
``` |
|
|
|
Note that the source map is not saved in a file, it's just returned in |
|
`result.map`. The value passed for `sourceMap.url` is only used to set |
|
`//# sourceMappingURL=out.js.map` in `result.code`. The value of |
|
`filename` is only used to set `file` attribute (see [the spec][sm-spec]) |
|
in source map file. |
|
|
|
You can set option `sourceMap.url` to be `"inline"` and source map will |
|
be appended to code. |
|
|
|
You can also specify sourceRoot property to be included in source map: |
|
```javascript |
|
var result = await minify({"file1.js": "var a = function() {};"}, { |
|
sourceMap: { |
|
root: "http://example.com/src", |
|
url: "out.js.map" |
|
} |
|
}); |
|
``` |
|
|
|
If you're compressing compiled JavaScript and have a source map for it, you |
|
can use `sourceMap.content`: |
|
```javascript |
|
var result = await minify({"compiled.js": "compiled code"}, { |
|
sourceMap: { |
|
content: "content from compiled.js.map", |
|
url: "minified.js.map" |
|
} |
|
}); |
|
// same as before, it returns `code` and `map` |
|
``` |
|
|
|
If you're using the `X-SourceMap` header instead, you can just omit `sourceMap.url`. |
|
|
|
If you happen to need the source map as a raw object, set `sourceMap.asObject` to `true`. |
|
|
|
## Parse options |
|
|
|
- `bare_returns` (default `false`) -- support top level `return` statements |
|
|
|
- `html5_comments` (default `true`) |
|
|
|
- `shebang` (default `true`) -- support `#!command` as the first line |
|
|
|
- `spidermonkey` (default `false`) -- accept a Spidermonkey (Mozilla) AST |
|
|
|
## Compress options |
|
|
|
- `defaults` (default: `true`) -- Pass `false` to disable most default |
|
enabled `compress` transforms. Useful when you only want to enable a few |
|
`compress` options while disabling the rest. |
|
|
|
- `arrows` (default: `true`) -- Class and object literal methods are converted |
|
will also be converted to arrow expressions if the resultant code is shorter: |
|
`m(){return x}` becomes `m:()=>x`. To do this to regular ES5 functions which |
|
don't use `this` or `arguments`, see `unsafe_arrows`. |
|
|
|
- `arguments` (default: `false`) -- replace `arguments[index]` with function |
|
parameter name whenever possible. |
|
|
|
- `booleans` (default: `true`) -- various optimizations for boolean context, |
|
for example `!!a ? b : c → a ? b : c` |
|
|
|
- `booleans_as_integers` (default: `false`) -- Turn booleans into 0 and 1, also |
|
makes comparisons with booleans use `==` and `!=` instead of `===` and `!==`. |
|
|
|
- `collapse_vars` (default: `true`) -- Collapse single-use non-constant variables, |
|
side effects permitting. |
|
|
|
- `comparisons` (default: `true`) -- apply certain optimizations to binary nodes, |
|
e.g. `!(a <= b) → a > b` (only when `unsafe_comps`), attempts to negate binary |
|
nodes, e.g. `a = !b && !c && !d && !e → a=!(b||c||d||e)` etc. |
|
|
|
- `computed_props` (default: `true`) -- Transforms constant computed properties |
|
into regular ones: `{["computed"]: 1}` is converted to `{computed: 1}`. |
|
|
|
- `conditionals` (default: `true`) -- apply optimizations for `if`-s and conditional |
|
expressions |
|
|
|
- `dead_code` (default: `true`) -- remove unreachable code |
|
|
|
- `directives` (default: `true`) -- remove redundant or non-standard directives |
|
|
|
- `drop_console` (default: `false`) -- Pass `true` to discard calls to |
|
`console.*` functions. If you wish to drop a specific function call |
|
such as `console.info` and/or retain side effects from function arguments |
|
after dropping the function call then use `pure_funcs` instead. |
|
|
|
- `drop_debugger` (default: `true`) -- remove `debugger;` statements |
|
|
|
- `ecma` (default: `5`) -- Pass `2015` or greater to enable `compress` options that |
|
will transform ES5 code into smaller ES6+ equivalent forms. |
|
|
|
- `evaluate` (default: `true`) -- attempt to evaluate constant expressions |
|
|
|
- `expression` (default: `false`) -- Pass `true` to preserve completion values |
|
from terminal statements without `return`, e.g. in bookmarklets. |
|
|
|
- `global_defs` (default: `{}`) -- see [conditional compilation](#conditional-compilation) |
|
|
|
- `hoist_funs` (default: `false`) -- hoist function declarations |
|
|
|
- `hoist_props` (default: `true`) -- hoist properties from constant object and |
|
array literals into regular variables subject to a set of constraints. For example: |
|
`var o={p:1, q:2}; f(o.p, o.q);` is converted to `f(1, 2);`. Note: `hoist_props` |
|
works best with `mangle` enabled, the `compress` option `passes` set to `2` or higher, |
|
and the `compress` option `toplevel` enabled. |
|
|
|
- `hoist_vars` (default: `false`) -- hoist `var` declarations (this is `false` |
|
by default because it seems to increase the size of the output in general) |
|
|
|
- `if_return` (default: `true`) -- optimizations for if/return and if/continue |
|
|
|
- `inline` (default: `true`) -- inline calls to function with simple/`return` statement: |
|
- `false` -- same as `0` |
|
- `0` -- disabled inlining |
|
- `1` -- inline simple functions |
|
- `2` -- inline functions with arguments |
|
- `3` -- inline functions with arguments and variables |
|
- `true` -- same as `3` |
|
|
|
- `join_vars` (default: `true`) -- join consecutive `var` statements |
|
|
|
- `keep_classnames` (default: `false`) -- Pass `true` to prevent the compressor from |
|
discarding class names. Pass a regular expression to only keep class names matching |
|
that regex. See also: the `keep_classnames` [mangle option](#mangle-options). |
|
|
|
- `keep_fargs` (default: `true`) -- Prevents the compressor from discarding unused |
|
function arguments. You need this for code which relies on `Function.length`. |
|
|
|
- `keep_fnames` (default: `false`) -- Pass `true` to prevent the |
|
compressor from discarding function names. Pass a regular expression to only keep |
|
function names matching that regex. Useful for code relying on `Function.prototype.name`. |
|
See also: the `keep_fnames` [mangle option](#mangle-options). |
|
|
|
- `keep_infinity` (default: `false`) -- Pass `true` to prevent `Infinity` from |
|
being compressed into `1/0`, which may cause performance issues on Chrome. |
|
|
|
- `loops` (default: `true`) -- optimizations for `do`, `while` and `for` loops |
|
when we can statically determine the condition. |
|
|
|
- `module` (default `false`) -- Pass `true` when compressing an ES6 module. Strict |
|
mode is implied and the `toplevel` option as well. |
|
|
|
- `negate_iife` (default: `true`) -- negate "Immediately-Called Function Expressions" |
|
where the return value is discarded, to avoid the parens that the |
|
code generator would insert. |
|
|
|
- `passes` (default: `1`) -- The maximum number of times to run compress. |
|
In some cases more than one pass leads to further compressed code. Keep in |
|
mind more passes will take more time. |
|
|
|
- `properties` (default: `true`) -- rewrite property access using the dot notation, for |
|
example `foo["bar"] → foo.bar` |
|
|
|
- `pure_funcs` (default: `null`) -- You can pass an array of names and |
|
Terser will assume that those functions do not produce side |
|
effects. DANGER: will not check if the name is redefined in scope. |
|
An example case here, for instance `var q = Math.floor(a/b)`. If |
|
variable `q` is not used elsewhere, Terser will drop it, but will |
|
still keep the `Math.floor(a/b)`, not knowing what it does. You can |
|
pass `pure_funcs: [ 'Math.floor' ]` to let it know that this |
|
function won't produce any side effect, in which case the whole |
|
statement would get discarded. The current implementation adds some |
|
overhead (compression will be slower). |
|
|
|
- `pure_getters` (default: `"strict"`) -- If you pass `true` for |
|
this, Terser will assume that object property access |
|
(e.g. `foo.bar` or `foo["bar"]`) doesn't have any side effects. |
|
Specify `"strict"` to treat `foo.bar` as side-effect-free only when |
|
`foo` is certain to not throw, i.e. not `null` or `undefined`. |
|
|
|
- `reduce_vars` (default: `true`) -- Improve optimization on variables assigned with and |
|
used as constant values. |
|
|
|
- `reduce_funcs` (default: `true`) -- Inline single-use functions when |
|
possible. Depends on `reduce_vars` being enabled. Disabling this option |
|
sometimes improves performance of the output code. |
|
|
|
- `sequences` (default: `true`) -- join consecutive simple statements using the |
|
comma operator. May be set to a positive integer to specify the maximum number |
|
of consecutive comma sequences that will be generated. If this option is set to |
|
`true` then the default `sequences` limit is `200`. Set option to `false` or `0` |
|
to disable. The smallest `sequences` length is `2`. A `sequences` value of `1` |
|
is grandfathered to be equivalent to `true` and as such means `200`. On rare |
|
occasions the default sequences limit leads to very slow compress times in which |
|
case a value of `20` or less is recommended. |
|
|
|
- `side_effects` (default: `true`) -- Remove expressions which have no side effects |
|
and whose results aren't used. |
|
|
|
- `switches` (default: `true`) -- de-duplicate and remove unreachable `switch` branches |
|
|
|
- `toplevel` (default: `false`) -- drop unreferenced functions (`"funcs"`) and/or |
|
variables (`"vars"`) in the top level scope (`false` by default, `true` to drop |
|
both unreferenced functions and variables) |
|
|
|
- `top_retain` (default: `null`) -- prevent specific toplevel functions and |
|
variables from `unused` removal (can be array, comma-separated, RegExp or |
|
function. Implies `toplevel`) |
|
|
|
- `typeofs` (default: `true`) -- Transforms `typeof foo == "undefined"` into |
|
`foo === void 0`. Note: recommend to set this value to `false` for IE10 and |
|
earlier versions due to known issues. |
|
|
|
- `unsafe` (default: `false`) -- apply "unsafe" transformations |
|
([details](#the-unsafe-compress-option)). |
|
|
|
- `unsafe_arrows` (default: `false`) -- Convert ES5 style anonymous function |
|
expressions to arrow functions if the function body does not reference `this`. |
|
Note: it is not always safe to perform this conversion if code relies on the |
|
the function having a `prototype`, which arrow functions lack. |
|
This transform requires that the `ecma` compress option is set to `2015` or greater. |
|
|
|
- `unsafe_comps` (default: `false`) -- Reverse `<` and `<=` to `>` and `>=` to |
|
allow improved compression. This might be unsafe when an at least one of two |
|
operands is an object with computed values due the use of methods like `get`, |
|
or `valueOf`. This could cause change in execution order after operands in the |
|
comparison are switching. Compression only works if both `comparisons` and |
|
`unsafe_comps` are both set to true. |
|
|
|
- `unsafe_Function` (default: `false`) -- compress and mangle `Function(args, code)` |
|
when both `args` and `code` are string literals. |
|
|
|
- `unsafe_math` (default: `false`) -- optimize numerical expressions like |
|
`2 * x * 3` into `6 * x`, which may give imprecise floating point results. |
|
|
|
- `unsafe_symbols` (default: `false`) -- removes keys from native Symbol |
|
declarations, e.g `Symbol("kDog")` becomes `Symbol()`. |
|
|
|
- `unsafe_methods` (default: false) -- Converts `{ m: function(){} }` to |
|
`{ m(){} }`. `ecma` must be set to `6` or greater to enable this transform. |
|
If `unsafe_methods` is a RegExp then key/value pairs with keys matching the |
|
RegExp will be converted to concise methods. |
|
Note: if enabled there is a risk of getting a "`<method name>` is not a |
|
constructor" TypeError should any code try to `new` the former function. |
|
|
|
- `unsafe_proto` (default: `false`) -- optimize expressions like |
|
`Array.prototype.slice.call(a)` into `[].slice.call(a)` |
|
|
|
- `unsafe_regexp` (default: `false`) -- enable substitutions of variables with |
|
`RegExp` values the same way as if they are constants. |
|
|
|
- `unsafe_undefined` (default: `false`) -- substitute `void 0` if there is a |
|
variable named `undefined` in scope (variable name will be mangled, typically |
|
reduced to a single character) |
|
|
|
- `unused` (default: `true`) -- drop unreferenced functions and variables (simple |
|
direct variable assignments do not count as references unless set to `"keep_assign"`) |
|
|
|
## Mangle options |
|
|
|
- `eval` (default `false`) -- Pass `true` to mangle names visible in scopes |
|
where `eval` or `with` are used. |
|
|
|
- `keep_classnames` (default `false`) -- Pass `true` to not mangle class names. |
|
Pass a regular expression to only keep class names matching that regex. |
|
See also: the `keep_classnames` [compress option](#compress-options). |
|
|
|
- `keep_fnames` (default `false`) -- Pass `true` to not mangle function names. |
|
Pass a regular expression to only keep function names matching that regex. |
|
Useful for code relying on `Function.prototype.name`. See also: the `keep_fnames` |
|
[compress option](#compress-options). |
|
|
|
- `module` (default `false`) -- Pass `true` an ES6 modules, where the toplevel |
|
scope is not the global scope. Implies `toplevel`. |
|
|
|
- `nth_identifier` (default: an internal mangler that weights based on character |
|
frequency analysis) -- Pass an object with a `get(n)` function that converts an |
|
ordinal into the nth most favored (usually shortest) identifier. |
|
Optionally also provide `reset()`, `sort()`, and `consider(chars, delta)` to |
|
use character frequency analysis of the source code. |
|
|
|
- `reserved` (default `[]`) -- Pass an array of identifiers that should be |
|
excluded from mangling. Example: `["foo", "bar"]`. |
|
|
|
- `toplevel` (default `false`) -- Pass `true` to mangle names declared in the |
|
top level scope. |
|
|
|
- `safari10` (default `false`) -- Pass `true` to work around the Safari 10 loop |
|
iterator [bug](https://bugs.webkit.org/show_bug.cgi?id=171041) |
|
"Cannot declare a let variable twice". |
|
See also: the `safari10` [format option](#format-options). |
|
|
|
Examples: |
|
|
|
```javascript |
|
// test.js |
|
var globalVar; |
|
function funcName(firstLongName, anotherLongName) { |
|
var myVariable = firstLongName + anotherLongName; |
|
} |
|
``` |
|
```javascript |
|
var code = fs.readFileSync("test.js", "utf8"); |
|
|
|
await minify(code).code; |
|
// 'function funcName(a,n){}var globalVar;' |
|
|
|
await minify(code, { mangle: { reserved: ['firstLongName'] } }).code; |
|
// 'function funcName(firstLongName,a){}var globalVar;' |
|
|
|
await minify(code, { mangle: { toplevel: true } }).code; |
|
// 'function n(n,a){}var a;' |
|
``` |
|
|
|
### Mangle properties options |
|
|
|
- `builtins` (default: `false`) — Use `true` to allow the mangling of builtin |
|
DOM properties. Not recommended to override this setting. |
|
|
|
- `debug` (default: `false`) — Mangle names with the original name still present. |
|
Pass an empty string `""` to enable, or a non-empty string to set the debug suffix. |
|
|
|
- `keep_quoted` (default: `false`) — How quoting properties (`{"prop": ...}` and `obj["prop"]`) controls what gets mangled. |
|
- `"strict"` (recommended) -- `obj.prop` is mangled. |
|
- `false` -- `obj["prop"]` is mangled. |
|
- `true` -- `obj.prop` is mangled unless there is `obj["prop"]` elsewhere in the code. |
|
|
|
- `nth_identifer` (default: an internal mangler that weights based on character |
|
frequency analysis) -- Pass an object with a `get(n)` function that converts an |
|
ordinal into the nth most favored (usually shortest) identifier. |
|
Optionally also provide `reset()`, `sort()`, and `consider(chars, delta)` to |
|
use character frequency analysis of the source code. |
|
|
|
- `regex` (default: `null`) — Pass a [RegExp literal or pattern string](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp) to only mangle property matching the regular expression. |
|
|
|
- `reserved` (default: `[]`) — Do not mangle property names listed in the |
|
`reserved` array. |
|
|
|
- `undeclared` (default: `false`) - Mangle those names when they are accessed |
|
as properties of known top level variables but their declarations are never |
|
found in input code. May be useful when only minifying parts of a project. |
|
See [#397](https://github.com/terser/terser/issues/397) for more details. |
|
|
|
|
|
## Format options |
|
|
|
These options control the format of Terser's output code. Previously known |
|
as "output options". |
|
|
|
- `ascii_only` (default `false`) -- escape Unicode characters in strings and |
|
regexps (affects directives with non-ascii characters becoming invalid) |
|
|
|
- `beautify` (default `false`) -- (DEPRECATED) whether to beautify the output. |
|
When using the legacy `-b` CLI flag, this is set to true by default. |
|
|
|
- `braces` (default `false`) -- always insert braces in `if`, `for`, |
|
`do`, `while` or `with` statements, even if their body is a single |
|
statement. |
|
|
|
- `comments` (default `"some"`) -- by default it keeps JSDoc-style comments |
|
that contain "@license", "@copyright", "@preserve" or start with `!`, pass `true` |
|
or `"all"` to preserve all comments, `false` to omit comments in the output, |
|
a regular expression string (e.g. `/^!/`) or a function. |
|
|
|
- `ecma` (default `5`) -- set desired EcmaScript standard version for output. |
|
Set `ecma` to `2015` or greater to emit shorthand object properties - i.e.: |
|
`{a}` instead of `{a: a}`. The `ecma` option will only change the output in |
|
direct control of the beautifier. Non-compatible features in your input will |
|
still be output as is. For example: an `ecma` setting of `5` will **not** |
|
convert modern code to ES5. |
|
|
|
- `indent_level` (default `4`) |
|
|
|
- `indent_start` (default `0`) -- prefix all lines by that many spaces |
|
|
|
- `inline_script` (default `true`) -- escape HTML comments and the slash in |
|
occurrences of `</script>` in strings |
|
|
|
- `keep_numbers` (default `false`) -- keep number literals as it was in original code |
|
(disables optimizations like converting `1000000` into `1e6`) |
|
|
|
- `keep_quoted_props` (default `false`) -- when turned on, prevents stripping |
|
quotes from property names in object literals. |
|
|
|
- `max_line_len` (default `false`) -- maximum line length (for minified code) |
|
|
|
- `preamble` (default `null`) -- when passed it must be a string and |
|
it will be prepended to the output literally. The source map will |
|
adjust for this text. Can be used to insert a comment containing |
|
licensing information, for example. |
|
|
|
- `quote_keys` (default `false`) -- pass `true` to quote all keys in literal |
|
objects |
|
|
|
- `quote_style` (default `0`) -- preferred quote style for strings (affects |
|
quoted property names and directives as well): |
|
- `0` -- prefers double quotes, switches to single quotes when there are |
|
more double quotes in the string itself. `0` is best for gzip size. |
|
- `1` -- always use single quotes |
|
- `2` -- always use double quotes |
|
- `3` -- always use the original quotes |
|
|
|
- `preserve_annotations` -- (default `false`) -- Preserve [Terser annotations](#annotations) in the output. |
|
|
|
- `safari10` (default `false`) -- set this option to `true` to work around |
|
the [Safari 10/11 await bug](https://bugs.webkit.org/show_bug.cgi?id=176685). |
|
See also: the `safari10` [mangle option](#mangle-options). |
|
|
|
- `semicolons` (default `true`) -- separate statements with semicolons. If |
|
you pass `false` then whenever possible we will use a newline instead of a |
|
semicolon, leading to more readable output of minified code (size before |
|
gzip could be smaller; size after gzip insignificantly larger). |
|
|
|
- `shebang` (default `true`) -- preserve shebang `#!` in preamble (bash scripts) |
|
|
|
- `spidermonkey` (default `false`) -- produce a Spidermonkey (Mozilla) AST |
|
|
|
- `webkit` (default `false`) -- enable workarounds for WebKit bugs. |
|
PhantomJS users should set this option to `true`. |
|
|
|
- `wrap_iife` (default `false`) -- pass `true` to wrap immediately invoked |
|
function expressions. See |
|
[#640](https://github.com/mishoo/UglifyJS2/issues/640) for more details. |
|
|
|
- `wrap_func_args` (default `true`) -- pass `false` if you do not want to wrap |
|
function expressions that are passed as arguments, in parenthesis. See |
|
[OptimizeJS](https://github.com/nolanlawson/optimize-js) for more details. |
|
|
|
# Miscellaneous |
|
|
|
### Keeping copyright notices or other comments |
|
|
|
You can pass `--comments` to retain certain comments in the output. By |
|
default it will keep comments starting with "!" and JSDoc-style comments that |
|
contain "@preserve", "@copyright", "@license" or "@cc_on" (conditional compilation for IE). |
|
You can pass `--comments all` to keep all the comments, or a valid JavaScript regexp to |
|
keep only comments that match this regexp. For example `--comments /^!/` |
|
will keep comments like `/*! Copyright Notice */`. |
|
|
|
Note, however, that there might be situations where comments are lost. For |
|
example: |
|
```javascript |
|
function f() { |
|
/** @preserve Foo Bar */ |
|
function g() { |
|
// this function is never called |
|
} |
|
return something(); |
|
} |
|
``` |
|
|
|
Even though it has "@preserve", the comment will be lost because the inner |
|
function `g` (which is the AST node to which the comment is attached to) is |
|
discarded by the compressor as not referenced. |
|
|
|
The safest comments where to place copyright information (or other info that |
|
needs to be kept in the output) are comments attached to toplevel nodes. |
|
|
|
### The `unsafe` `compress` option |
|
|
|
It enables some transformations that *might* break code logic in certain |
|
contrived cases, but should be fine for most code. It assumes that standard |
|
built-in ECMAScript functions and classes have not been altered or replaced. |
|
You might want to try it on your own code; it should reduce the minified size. |
|
Some examples of the optimizations made when this option is enabled: |
|
|
|
- `new Array(1, 2, 3)` or `Array(1, 2, 3)` → `[ 1, 2, 3 ]` |
|
- `Array.from([1, 2, 3])` → `[1, 2, 3]` |
|
- `new Object()` → `{}` |
|
- `String(exp)` or `exp.toString()` → `"" + exp` |
|
- `new Object/RegExp/Function/Error/Array (...)` → we discard the `new` |
|
- `"foo bar".substr(4)` → `"bar"` |
|
|
|
### Conditional compilation |
|
|
|
You can use the `--define` (`-d`) switch in order to declare global |
|
variables that Terser will assume to be constants (unless defined in |
|
scope). For example if you pass `--define DEBUG=false` then, coupled with |
|
dead code removal Terser will discard the following from the output: |
|
```javascript |
|
if (DEBUG) { |
|
console.log("debug stuff"); |
|
} |
|
``` |
|
|
|
You can specify nested constants in the form of `--define env.DEBUG=false`. |
|
|
|
Another way of doing that is to declare your globals as constants in a |
|
separate file and include it into the build. For example you can have a |
|
`build/defines.js` file with the following: |
|
```javascript |
|
var DEBUG = false; |
|
var PRODUCTION = true; |
|
// etc. |
|
``` |
|
|
|
and build your code like this: |
|
|
|
terser build/defines.js js/foo.js js/bar.js... -c |
|
|
|
Terser will notice the constants and, since they cannot be altered, it |
|
will evaluate references to them to the value itself and drop unreachable |
|
code as usual. The build will contain the `const` declarations if you use |
|
them. If you are targeting < ES6 environments which does not support `const`, |
|
using `var` with `reduce_vars` (enabled by default) should suffice. |
|
|
|
### Conditional compilation API |
|
|
|
You can also use conditional compilation via the programmatic API. With the difference that the |
|
property name is `global_defs` and is a compressor property: |
|
|
|
```javascript |
|
var result = await minify(fs.readFileSync("input.js", "utf8"), { |
|
compress: { |
|
dead_code: true, |
|
global_defs: { |
|
DEBUG: false |
|
} |
|
} |
|
}); |
|
``` |
|
|
|
To replace an identifier with an arbitrary non-constant expression it is |
|
necessary to prefix the `global_defs` key with `"@"` to instruct Terser |
|
to parse the value as an expression: |
|
```javascript |
|
await minify("alert('hello');", { |
|
compress: { |
|
global_defs: { |
|
"@alert": "console.log" |
|
} |
|
} |
|
}).code; |
|
// returns: 'console.log("hello");' |
|
``` |
|
|
|
Otherwise it would be replaced as string literal: |
|
```javascript |
|
await minify("alert('hello');", { |
|
compress: { |
|
global_defs: { |
|
"alert": "console.log" |
|
} |
|
} |
|
}).code; |
|
// returns: '"console.log"("hello");' |
|
``` |
|
|
|
### Annotations |
|
|
|
Annotations in Terser are a way to tell it to treat a certain function call differently. The following annotations are available: |
|
|
|
* `/*@__INLINE__*/` - forces a function to be inlined somewhere. |
|
* `/*@__NOINLINE__*/` - Makes sure the called function is not inlined into the call site. |
|
* `/*@__PURE__*/` - Marks a function call as pure. That means, it can safely be dropped. |
|
|
|
You can use either a `@` sign at the start, or a `#`. |
|
|
|
Here are some examples on how to use them: |
|
|
|
```javascript |
|
/*@__INLINE__*/ |
|
function_always_inlined_here() |
|
|
|
/*#__NOINLINE__*/ |
|
function_cant_be_inlined_into_here() |
|
|
|
const x = /*#__PURE__*/i_am_dropped_if_x_is_not_used() |
|
``` |
|
|
|
### ESTree / SpiderMonkey AST |
|
|
|
Terser has its own abstract syntax tree format; for |
|
[practical reasons](http://lisperator.net/blog/uglifyjs-why-not-switching-to-spidermonkey-ast/) |
|
we can't easily change to using the SpiderMonkey AST internally. However, |
|
Terser now has a converter which can import a SpiderMonkey AST. |
|
|
|
For example [Acorn][acorn] is a super-fast parser that produces a |
|
SpiderMonkey AST. It has a small CLI utility that parses one file and dumps |
|
the AST in JSON on the standard output. To use Terser to mangle and |
|
compress that: |
|
|
|
acorn file.js | terser -p spidermonkey -m -c |
|
|
|
The `-p spidermonkey` option tells Terser that all input files are not |
|
JavaScript, but JS code described in SpiderMonkey AST in JSON. Therefore we |
|
don't use our own parser in this case, but just transform that AST into our |
|
internal AST. |
|
|
|
`spidermonkey` is also available in `minify` as `parse` and `format` options to |
|
accept and/or produce a spidermonkey AST. |
|
|
|
### Use Acorn for parsing |
|
|
|
More for fun, I added the `-p acorn` option which will use Acorn to do all |
|
the parsing. If you pass this option, Terser will `require("acorn")`. |
|
|
|
Acorn is really fast (e.g. 250ms instead of 380ms on some 650K code), but |
|
converting the SpiderMonkey tree that Acorn produces takes another 150ms so |
|
in total it's a bit more than just using Terser's own parser. |
|
|
|
[acorn]: https://github.com/ternjs/acorn |
|
[sm-spec]: https://docs.google.com/document/d/1U1RGAehQwRypUTovF1KRlpiOFze0b-_2gc6fAH0KY0k |
|
|
|
### Terser Fast Minify Mode |
|
|
|
It's not well known, but whitespace removal and symbol mangling accounts |
|
for 95% of the size reduction in minified code for most JavaScript - not |
|
elaborate code transforms. One can simply disable `compress` to speed up |
|
Terser builds by 3 to 4 times. |
|
|
|
| d3.js | size | gzip size | time (s) | |
|
| --- | ---: | ---: | ---: | |
|
| original | 451,131 | 108,733 | - | |
|
| terser@3.7.5 mangle=false, compress=false | 316,600 | 85,245 | 0.82 | |
|
| terser@3.7.5 mangle=true, compress=false | 220,216 | 72,730 | 1.45 | |
|
| terser@3.7.5 mangle=true, compress=true | 212,046 | 70,954 | 5.87 | |
|
| babili@0.1.4 | 210,713 | 72,140 | 12.64 | |
|
| babel-minify@0.4.3 | 210,321 | 72,242 | 48.67 | |
|
| babel-minify@0.5.0-alpha.01eac1c3 | 210,421 | 72,238 | 14.17 | |
|
|
|
To enable fast minify mode from the CLI use: |
|
``` |
|
terser file.js -m |
|
``` |
|
To enable fast minify mode with the API use: |
|
```js |
|
await minify(code, { compress: false, mangle: true }); |
|
``` |
|
|
|
#### Source maps and debugging |
|
|
|
Various `compress` transforms that simplify, rearrange, inline and remove code |
|
are known to have an adverse effect on debugging with source maps. This is |
|
expected as code is optimized and mappings are often simply not possible as |
|
some code no longer exists. For highest fidelity in source map debugging |
|
disable the `compress` option and just use `mangle`. |
|
|
|
### Compiler assumptions |
|
|
|
To allow for better optimizations, the compiler makes various assumptions: |
|
|
|
- `.toString()` and `.valueOf()` don't have side effects, and for built-in |
|
objects they have not been overridden. |
|
- `undefined`, `NaN` and `Infinity` have not been externally redefined. |
|
- `arguments.callee`, `arguments.caller` and `Function.prototype.caller` are not used. |
|
- The code doesn't expect the contents of `Function.prototype.toString()` or |
|
`Error.prototype.stack` to be anything in particular. |
|
- Getting and setting properties on a plain object does not cause other side effects |
|
(using `.watch()` or `Proxy`). |
|
- Object properties can be added, removed and modified (not prevented with |
|
`Object.defineProperty()`, `Object.defineProperties()`, `Object.freeze()`, |
|
`Object.preventExtensions()` or `Object.seal()`). |
|
- `document.all` is not `== null` |
|
- Assigning properties to a class doesn't have side effects and does not throw. |
|
|
|
### Build Tools and Adaptors using Terser |
|
|
|
https://www.npmjs.com/browse/depended/terser |
|
|
|
### Replacing `uglify-es` with `terser` in a project using `yarn` |
|
|
|
A number of JS bundlers and uglify wrappers are still using buggy versions |
|
of `uglify-es` and have not yet upgraded to `terser`. If you are using `yarn` |
|
you can add the following alias to your project's `package.json` file: |
|
|
|
```js |
|
"resolutions": { |
|
"uglify-es": "npm:terser" |
|
} |
|
``` |
|
|
|
to use `terser` instead of `uglify-es` in all deeply nested dependencies |
|
without changing any code. |
|
|
|
Note: for this change to take effect you must run the following commands |
|
to remove the existing `yarn` lock file and reinstall all packages: |
|
|
|
``` |
|
$ rm -rf node_modules yarn.lock |
|
$ yarn |
|
``` |
|
|
|
<!-- API_REFERENCE:END --> |
|
|
|
# Reporting issues |
|
|
|
In the terser CLI we use [source-map-support](https://npmjs.com/source-map-support) to produce good error stacks. In your own app, you're expected to enable source-map-support (read their docs) to have nice stack traces that will help you write good issues. |
|
|
|
## Obtaining the source code given to Terser |
|
|
|
Because users often don't control the call to `await minify()` or its arguments, Terser provides a `TERSER_DEBUG_DIR` environment variable to make terser output some debug logs. If you're using a bundler or a project that includes a bundler and are not sure what went wrong with your code, pass that variable like so: |
|
|
|
``` |
|
$ TERSER_DEBUG_DIR=/path/to/logs command-that-uses-terser |
|
$ ls /path/to/logs |
|
terser-debug-123456.log |
|
``` |
|
|
|
If you're not sure how to set an environment variable on your shell (the above example works in bash), you can try using cross-env: |
|
|
|
``` |
|
> npx cross-env TERSER_DEBUG_DIR=/path/to/logs command-that-uses-terser |
|
``` |
|
|
|
# README.md Patrons: |
|
|
|
*note*: You can support this project on patreon: <a target="_blank" rel="nofollow" href="https://www.patreon.com/fabiosantoscode"><img src="https://c5.patreon.com/external/logo/become_a_patron_button@2x.png" alt="patron" width="100px" height="auto"></a>. Check out [PATRONS.md](https://github.com/terser/terser/blob/master/PATRONS.md) for our first-tier patrons. |
|
|
|
These are the second-tier patrons. Great thanks for your support! |
|
|
|
* CKEditor ![](https://c10.patreonusercontent.com/3/eyJoIjoxMDAsInciOjEwMH0%3D/patreon-media/p/user/15452278/f8548dcf48d740619071e8d614459280/1?token-time=2145916800&token-hash=SIQ54PhIPHv3M7CVz9LxS8_8v4sOw4H304HaXsXj8MM%3D) |
|
* 38elements ![](https://c10.patreonusercontent.com/3/eyJ3IjoyMDB9/patreon-media/p/user/12501844/88e7fc5dd62d45c6a5626533bbd48cfb/1?token-time=2145916800&token-hash=c3AsQ5T0IQWic0zKxFHu-bGGQJkXQFvafvJ4bPerFR4%3D) |
|
|
|
## Contributors |
|
|
|
### Code Contributors |
|
|
|
This project exists thanks to all the people who contribute. [[Contribute](CONTRIBUTING.md)]. |
|
<a href="https://github.com/terser/terser/graphs/contributors"><img src="https://opencollective.com/terser/contributors.svg?width=890&button=false" /></a> |
|
|
|
### Financial Contributors |
|
|
|
Become a financial contributor and help us sustain our community. [[Contribute](https://opencollective.com/terser/contribute)] |
|
|
|
#### Individuals |
|
|
|
<a href="https://opencollective.com/terser"><img src="https://opencollective.com/terser/individuals.svg?width=890"></a> |
|
|
|
#### Organizations |
|
|
|
Support this project with your organization. Your logo will show up here with a link to your website. [[Contribute](https://opencollective.com/terser/contribute)] |
|
|
|
<a href="https://opencollective.com/terser/organization/0/website"><img src="https://opencollective.com/terser/organization/0/avatar.svg"></a> |
|
<a href="https://opencollective.com/terser/organization/1/website"><img src="https://opencollective.com/terser/organization/1/avatar.svg"></a> |
|
<a href="https://opencollective.com/terser/organization/2/website"><img src="https://opencollective.com/terser/organization/2/avatar.svg"></a> |
|
<a href="https://opencollective.com/terser/organization/3/website"><img src="https://opencollective.com/terser/organization/3/avatar.svg"></a> |
|
<a href="https://opencollective.com/terser/organization/4/website"><img src="https://opencollective.com/terser/organization/4/avatar.svg"></a> |
|
<a href="https://opencollective.com/terser/organization/5/website"><img src="https://opencollective.com/terser/organization/5/avatar.svg"></a> |
|
<a href="https://opencollective.com/terser/organization/6/website"><img src="https://opencollective.com/terser/organization/6/avatar.svg"></a> |
|
<a href="https://opencollective.com/terser/organization/7/website"><img src="https://opencollective.com/terser/organization/7/avatar.svg"></a> |
|
<a href="https://opencollective.com/terser/organization/8/website"><img src="https://opencollective.com/terser/organization/8/avatar.svg"></a> |
|
<a href="https://opencollective.com/terser/organization/9/website"><img src="https://opencollective.com/terser/organization/9/avatar.svg"></a>
|
|
|