你与弄懂promise之间可能只差这篇文章（二）

点我看看~话不多说，上源码：// 核心方法！核心方法！核心方法！也是最难懂的！—-STARTconst resolvePromise = (promise2, x, resolve, reject) => { if (promise2 === x) { return reject(new TypeError(“A promise cannot be resolved with itself”)) } if (x && (typeof x === “object” || typeof x === “function”)) { try { let then = x.then; if (typeof then === “function”) { then.call(x, y => { resolve(y); resolvePromise(promise2, y, resolve, reject); }, r => { reject(r); }) } else { resolve(x); } } catch (e) { reject(e) } } else { resolve(x) }};// 核心方法！核心方法！核心方法！也是最难懂的！—-END// Commitment就是class Commitment { constructor (executor) { this.status = “PENDING” this.value = void(0); this.reason = void(0); this.onResolvedCallbacks = []; this.onRejectedCallbacks = []; const resolve = (value) => { if (this.status === “PENDING”) { this.status = “RESOLVED”; this.value = value; this.onResolvedCallbacks.forEach(cb => cb()) } } const reject = (reason) => { if (this.status === “PENDING”) { this.status = “REJECTED”; this.reason = reason; this.onRejectedCallbacks.forEach(cb => cb()) } } try { executor(resolve, reject) } catch (e) { reject(e) } } then (onResolvedFn, onRejectedFn) { let promise2, x; promise2 = new Promise((resolve, reject) => { if (this.status === “RESOLVED”) { setTimeout(() => { try { x = onResolvedFn(this.value); resolvePromise(promise2, x, resolve, reject); } catch(e) { reject(e) } }, 0) } if (this.status === “REJECTED”) { setTimeout(() => { try { x = onRejectedFn(this.reason); resolvePromise(promise2, x, resolve, reject) } catch (e) { reject(e) } }, 0) } if (this.status === “PENDING”) { this.onResolvedCallbacks.push(() => { setTimeout(() => { try { x = onResolvedFn(this.value); resolvePromise(promise2, x, resolve, reject) } catch (e) { reject(e) } }, 0) }); this.onRejectedCallbacks.push(() => { setTimeout(() => { try { x = onRejectedFn(this.reason); resolvePromise(promise2, x, resolve, reject) } catch (e) { reject(e) } }, 0) }); } }); return promise2 } catch (onRejectedFn) { return this.then(null, onRejectedFn) } // 静态方法 static resolve (value) { return new Commitment((resolve, reject) => { resolve(value) }) } static reject (err) { return new Commitment((resolve, reject) => { reject(err) }) } static all () { let result = []; return new Commitment((resolve, reject) => { if (arguments.length === 0) { return reject(new TypeError(“undefined is not iterable (cannot read property Symbol(Symbol.iterator))”)) } else { let args = […arguments][0], result = []; let count = args.length, num = 0; for (let i = 0; i < count; i++) { let item = args[i]; try { let then = item.then; if (typeof then === “function”) { then.call(item, y => { num += 1; result[i] = y; if (num === count) { resolve(result) } }, r => { reject(r) }) } else { result[i] = item; if (num === count) { resolve(result) } } } catch (e) { reject(e) } } } }) } static race () { // 未完待续 }}