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214 lines
4.7 KiB
214 lines
4.7 KiB
2 years ago
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'use strict';
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var asap = require('asap');
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function noop() {}
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// States:
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//
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// 0 - pending
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// 1 - fulfilled with _value
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// 2 - rejected with _value
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// 3 - adopted the state of another promise, _value
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//
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// once the state is no longer pending (0) it is immutable
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// All `_` prefixed properties will be reduced to `_{random number}`
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// at build time to obfuscate them and discourage their use.
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// We don't use symbols or Object.defineProperty to fully hide them
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// because the performance isn't good enough.
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// to avoid using try/catch inside critical functions, we
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// extract them to here.
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var LAST_ERROR = null;
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var IS_ERROR = {};
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function getThen(obj) {
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try {
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return obj.then;
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} catch (ex) {
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LAST_ERROR = ex;
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return IS_ERROR;
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}
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}
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function tryCallOne(fn, a) {
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try {
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return fn(a);
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} catch (ex) {
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LAST_ERROR = ex;
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return IS_ERROR;
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}
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}
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function tryCallTwo(fn, a, b) {
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try {
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fn(a, b);
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} catch (ex) {
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LAST_ERROR = ex;
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return IS_ERROR;
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}
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}
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module.exports = Promise;
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function Promise(fn) {
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if (typeof this !== 'object') {
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throw new TypeError('Promises must be constructed via new');
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}
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if (typeof fn !== 'function') {
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throw new TypeError('Promise constructor\'s argument is not a function');
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}
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this._U = 0;
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this._V = 0;
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this._W = null;
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this._X = null;
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if (fn === noop) return;
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doResolve(fn, this);
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}
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Promise._Y = null;
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Promise._Z = null;
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Promise._0 = noop;
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Promise.prototype.then = function(onFulfilled, onRejected) {
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if (this.constructor !== Promise) {
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return safeThen(this, onFulfilled, onRejected);
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}
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var res = new Promise(noop);
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handle(this, new Handler(onFulfilled, onRejected, res));
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return res;
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};
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function safeThen(self, onFulfilled, onRejected) {
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return new self.constructor(function (resolve, reject) {
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var res = new Promise(noop);
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res.then(resolve, reject);
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handle(self, new Handler(onFulfilled, onRejected, res));
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});
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}
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function handle(self, deferred) {
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while (self._V === 3) {
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self = self._W;
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}
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if (Promise._Y) {
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Promise._Y(self);
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}
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if (self._V === 0) {
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if (self._U === 0) {
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self._U = 1;
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self._X = deferred;
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return;
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}
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if (self._U === 1) {
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self._U = 2;
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self._X = [self._X, deferred];
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return;
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}
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self._X.push(deferred);
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return;
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}
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handleResolved(self, deferred);
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}
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function handleResolved(self, deferred) {
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asap(function() {
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var cb = self._V === 1 ? deferred.onFulfilled : deferred.onRejected;
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if (cb === null) {
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if (self._V === 1) {
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resolve(deferred.promise, self._W);
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} else {
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reject(deferred.promise, self._W);
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}
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return;
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}
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var ret = tryCallOne(cb, self._W);
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if (ret === IS_ERROR) {
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reject(deferred.promise, LAST_ERROR);
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} else {
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resolve(deferred.promise, ret);
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}
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});
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}
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function resolve(self, newValue) {
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// Promise Resolution Procedure: https://github.com/promises-aplus/promises-spec#the-promise-resolution-procedure
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if (newValue === self) {
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return reject(
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self,
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new TypeError('A promise cannot be resolved with itself.')
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);
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}
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if (
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newValue &&
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(typeof newValue === 'object' || typeof newValue === 'function')
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) {
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var then = getThen(newValue);
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if (then === IS_ERROR) {
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return reject(self, LAST_ERROR);
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}
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if (
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then === self.then &&
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newValue instanceof Promise
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) {
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self._V = 3;
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self._W = newValue;
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finale(self);
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return;
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} else if (typeof then === 'function') {
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doResolve(then.bind(newValue), self);
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return;
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}
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}
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self._V = 1;
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self._W = newValue;
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finale(self);
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}
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function reject(self, newValue) {
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self._V = 2;
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self._W = newValue;
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if (Promise._Z) {
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Promise._Z(self, newValue);
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}
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finale(self);
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}
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function finale(self) {
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if (self._U === 1) {
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handle(self, self._X);
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self._X = null;
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}
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if (self._U === 2) {
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for (var i = 0; i < self._X.length; i++) {
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handle(self, self._X[i]);
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}
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self._X = null;
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}
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}
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function Handler(onFulfilled, onRejected, promise){
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this.onFulfilled = typeof onFulfilled === 'function' ? onFulfilled : null;
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this.onRejected = typeof onRejected === 'function' ? onRejected : null;
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this.promise = promise;
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}
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/**
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* Take a potentially misbehaving resolver function and make sure
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* onFulfilled and onRejected are only called once.
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*
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* Makes no guarantees about asynchrony.
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*/
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function doResolve(fn, promise) {
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var done = false;
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var res = tryCallTwo(fn, function (value) {
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if (done) return;
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done = true;
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resolve(promise, value);
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}, function (reason) {
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if (done) return;
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done = true;
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reject(promise, reason);
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});
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if (!done && res === IS_ERROR) {
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done = true;
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reject(promise, LAST_ERROR);
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}
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}
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