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| const STATE_MAPPING = { PENDING: 'pending', RESOLVED: 'resolved', REJECTED: 'rejected' };
class MyPromise { constructor(exector) { this.init(); const resolve = val => { if (this.status !== STATE_MAPPING.PENDING) { return; } this.status = STATE_MAPPING.RESOLVED; this.value = val; this.onResolvedCallbacks.forEach(fn => fn()); }; const reject = val => { if (this.status !== STATE_MAPPING.PENDING) { return; } this.status = STATE_MAPPING.REJECTED; this.value = val; this.onRejectedCallbacks.forEach(fn => fn()); };
try { exector(resolve, reject); } catch (error) { reject(error); } }
init() { this.status = STATE_MAPPING.PENDING; this.value = undefined; this.onResolvedCallbacks = []; this.onRejectedCallbacks = []; }
handleResolve(resolve, reject, handler) { try { const x = handler(this.value); if (x instanceof MyPromise) { x.then(resolve, reject); } else { resolve(x); } } catch (error) { reject(error); } }
handleReject(resolve, reject, handler) { try { const x = handler(this.value); if (x instanceof MyPromise) { x.then(resolve, reject); } else { resolve(x); } } catch (error) { reject(error); } }
then(onFulfilled, onRejected) { onFulfilled = typeof onFulfilled === 'function' ? onFulfilled : v => v; onRejected = typeof onRejected === 'function' ? onRejected : err => {throw err}; const actions = { resolved: () => { return new MyPromise((resolve, reject) => { setTimeout(() => { this.handleResolve(resolve, reject. onFulfilled); }, 0); }); }, rejectd: () => { return new MyPromise((resolve, reject) => { setTimeout(() => { this.handleReject(resolve, reject. onRejected); }, 0); }); }, pending: () => { return new MyPromise((resolve, reject) => { this.onResolvedCallbacks.push(() => { setTimeout(() => { this.handleResolve(resolve, reject, onFulfilled); }, 0); }); this.onRejectedCallbacks.push(() => { setTimeout(() => { this.handleReject(resolve, reject. onRejected); }, 0); }) }); } };
return actions[this.status](); } catch(onRejected) { this.then(undefined, onRejected); } static resolve(val) { return new MyPromise(resolve => resolve(val)); } static reject(reason) { return new MyPromise((resolve, reject) => reject(reason)); } static all(promises) { const arr = []; let i = 0; function processData(index, val, resolve) { arr[index] = val; i++; if (i === promises.length) { resolve(arr); } } return new MyPromise((resolve, reject) => { for (let index = 0; index < promises.length; index++) { const curPromise = promises[index]; curPromise.then((res) => { processData(index, res, resolve); }, err => { reject(err); }); } });
} static race (promises) { return new MyPromise((resolve, reject) => { for (let p of promises) { this.resolve(p).then(res => { resolve(res) }, err => { reject(err) }) } }); } }
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