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92 lines
2.5 KiB
92 lines
2.5 KiB
# import/no-cycle |
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Ensures that there is no resolvable path back to this module via its dependencies. |
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This includes cycles of depth 1 (imported module imports me) to `"∞"` (or `Infinity`), if the |
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[`maxDepth`](#maxdepth) option is not set. |
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```js |
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// dep-b.js |
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import './dep-a.js' |
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export function b() { /* ... */ } |
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``` |
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```js |
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// dep-a.js |
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import { b } from './dep-b.js' // reported: Dependency cycle detected. |
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``` |
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This rule does _not_ detect imports that resolve directly to the linted module; |
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for that, see [`no-self-import`]. |
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## Rule Details |
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### Options |
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By default, this rule only detects cycles for ES6 imports, but see the [`no-unresolved` options](./no-unresolved.md#options) as this rule also supports the same `commonjs` and `amd` flags. However, these flags only impact which import types are _linted_; the |
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import/export infrastructure only registers `import` statements in dependencies, so |
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cycles created by `require` within imported modules may not be detected. |
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#### `maxDepth` |
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There is a `maxDepth` option available to prevent full expansion of very deep dependency trees: |
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```js |
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/*eslint import/no-cycle: [2, { maxDepth: 1 }]*/ |
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// dep-c.js |
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import './dep-a.js' |
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``` |
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```js |
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// dep-b.js |
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import './dep-c.js' |
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export function b() { /* ... */ } |
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``` |
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```js |
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// dep-a.js |
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import { b } from './dep-b.js' // not reported as the cycle is at depth 2 |
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``` |
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This is not necessarily recommended, but available as a cost/benefit tradeoff mechanism |
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for reducing total project lint time, if needed. |
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#### `ignoreExternal` |
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An `ignoreExternal` option is available to prevent the cycle detection to expand to external modules: |
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```js |
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/*eslint import/no-cycle: [2, { ignoreExternal: true }]*/ |
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// dep-a.js |
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import 'module-b/dep-b.js' |
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export function a() { /* ... */ } |
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``` |
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```js |
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// node_modules/module-b/dep-b.js |
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import { a } from './dep-a.js' // not reported as this module is external |
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``` |
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Its value is `false` by default, but can be set to `true` for reducing total project lint time, if needed. |
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## When Not To Use It |
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This rule is comparatively computationally expensive. If you are pressed for lint |
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time, or don't think you have an issue with dependency cycles, you may not want |
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this rule enabled. |
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## Further Reading |
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- [Original inspiring issue](https://github.com/import-js/eslint-plugin-import/issues/941) |
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- Rule to detect that module imports itself: [`no-self-import`] |
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- [`import/external-module-folders`] setting |
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[`no-self-import`]: ./no-self-import.md |
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[`import/external-module-folders`]: ../../README.md#importexternal-module-folders
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