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213 lines
4.7 KiB
213 lines
4.7 KiB
'use strict'; |
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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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setImmediate(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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