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promise.js
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promise.js
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const PROMISE_STATUS = {
PENDING: 'PENDING',
FULFILLED: 'FULFILLED',
REJECTED: 'REJECTED',
};
function isPromise(val) {
if ((val !== null && typeof val === 'object') || typeof val === 'function') {
return typeof x.then === 'function';
}
return false;
}
function resolvePromise(promise2, x, resolve, reject) {
if (promise2 === x) {
reject(new TypeError('Chaining cycle detected for promise #<Promise>'));
}
let called;
if ((x !== null && typeof x === 'object') || typeof x === 'function') {
try {
let then = x.then;
if (typeof then === 'function') {
then.call(x, y => {
if (called) return;
called = true;
resolvePromise(promise2, y, resolve, reject);
}, r => {
if (called) return;
called = true;
reject(r);
});
} else {
resolve(x);
}
} catch (e) {
if (called) return;
called = true;
reject(e);
}
} else {
resolve(x);
}
}
class Promise {
constructor(executor) {
this.status = PROMISE_STATUS.PENDING;
this.value = undefined;
this.error = undefined;
this.onFulfilledCallbacks = [];
this.onRejectedCallbacks = [];
const resolve = value => {
if (value instanceof Promise) {
return value.then(resolve, reject);
}
if (this.status === PROMISE_STATUS.PENDING) {
this.status = PROMISE_STATUS.FULFILLED;
this.value = value;
this.onFulfilledCallbacks.forEach(cb => cb());
}
};
const reject = error => {
if (this.status === PROMISE_STATUS.PENDING) {
this.status = PROMISE_STATUS.REJECTED;
this.error = error;
this.onRejectedCallbacks.forEach(cb => cb());
}
};
try {
executor(resolve, reject);
} catch (e) {
reject(e);
}
}
then(onFulfilled, onRejected) {
onFulfilled = typeof onFulfilled === 'function' ? onFulfilled : val => val;
onRejected = typeof onRejected === 'function' ? onRejected : err => {throw err};
const promise2 = new Promise((resolve, reject) => {
if (this.status === PROMISE_STATUS.FULFILLED) {
setTimeout(() => {
try {
const x = onFulfilled(this.value);
resolvePromise(promise2, x, resolve, reject);
} catch (e) {
reject(e);
}
});
} else if (this.status === PROMISE_STATUS.REJECTED) {
setTimeout(() => {
try {
const x = onRejected(this.error);
resolvePromise(promise2, x, resolve, reject);
} catch (e) {
reject(e);
}
});
} else if (this.status === PROMISE_STATUS.PENDING) {
this.onFulfilledCallbacks.push(() => {
setTimeout(() => {
try {
const x = onFulfilled(this.value);
resolvePromise(promise2, x, resolve, reject);
} catch (e) {
reject(e);
}
});
});
this.onRejectedCallbacks.push(() => {
setTimeout(() => {
try {
const x = onRejected(this.error);
resolvePromise(promise2, x, resolve, reject);
} catch (e) {
reject(e);
}
});
});
}
});
return promise2;
}
catch(errorCallback) {
return this.then(null, errorCallback);
}
finally(callback) {
return this.then(value => {
return Promise.resolve(callback()).then(() => value);
}, error => {
return Promise.resolve(callback()).then(() => {throw error});
});
}
static all(promises) {
return new Promise((resolve, reject) => {
let arr = [];
let index = 0;
let processData = (i, y) => {
arr[i] = y;
if (++index === promises.length) {
resolve(arr);
}
};
for (let i = 0; i < promises.length; i++) {
let value = promises[i];
if (isPromise(value)) {
value.then(y => {
processData(i, y);
}, reject);
} else {
processData(i, value);
}
}
});
}
static race(promises) {
return new Promise((resolve, reject) => {
for(let i = 0; i < promises.length; i++) {
const value = promises[i];
if (isPromise(value)) {
value.then(resolve, reject);
} else {
resolve(value);
}
}
});
}
static resolve(value) {
return new Promise((resolve, reject) => {
resolve(value);
});
}
static reject(error) {
return new Promise((resolve, reject) => {
reject(error);
});
}
}
Promise.defer = Promise.deferred = function() {
let dfd = {};
dfd.promise = new Promise((resolve, reject) => {
dfd.resolve = resolve;
dfd.reject = reject;
});
return dfd;
};
// promises-aplus-tests promise.js 执行该命令测试Promise
module.exports = Promise;