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MyPromise.js
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MyPromise.js
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const PENDING = 'pending';
const FULFILLED = 'fulfilled';
const REJECTED = 'rejected';
class MyPromise {
static resolve(val) {
return new MyPromise((resolve, reject) => {
resolve(val)
})
}
//reject方法
static reject(val) {
return new MyPromise((resolve, reject) => {
reject(val)
})
}
static all(promiseArr) {
return new MyPromise((resolve, reject) => {
let result = [];
promiseArr.forEach((promise, index) => {
promise.then((value) => {
result[index] = value;
if (result.length === promiseArr.length) {
resolve(result);
}
}, reject);
});
});
}
static race(promiseArr) {
return new MyPromise((resolve, reject) => {
promiseArr.forEach(promise => {
promise.then((value) => {
resolve(value);
}, (err) => reject(err));
});
});
}
static deferred() {
let dfd = {};
dfd.promies = new MyPromise((resolve, reject) => {
dfd.resolve = resolve;
dfd.rfeject = reject;
});
return dfd;
};
constructor(executor) {
this.state = PENDING;
this.value = null;
this.reason = null;
// 存放成功回调的函数
this.onFulfilledCallbacks = [];
// 存放失败回调的函数
this.onRejectedCallbacks = [];
const resolve = value => {
if (this.state === PENDING) {
this.value = value;
this.state = FULFILLED;
this.onFulfilledCallbacks.map(fn => fn());
}
}
const reject = value => {
if (this.state === PENDING) {
this.reason = value;
this.state = REJECTED;
this.onRejectedCallbacks.map(fn => fn());
}
}
try {
executor(resolve, reject);
} catch (error) {
reject(error);
}
}
then(onFulfilled, onRejected) {
let self = this;
let promise2 = null;
//解决onFulfilled,onRejected没有传值的问题
onFulfilled = typeof onFulfilled === 'function' ? onFulfilled : y => y
//因为错误的值要让后面访问到,所以这里也要跑出个错误,不然会在之后then的resolve中捕获
onRejected = typeof onRejected === 'function' ? onRejected : err => {
throw err;
}
promise2 = new MyPromise((resolve, reject) => {
if (self.state === PENDING) {
self.onFulfilledCallbacks.push(() => {
setTimeout(() => {
try {
let x = onFulfilled(self.value);
self.resolvePromise(promise2, x, resolve, reject);
} catch (reason) {
reject(reason);
}
}, 0)
});
self.onRejectedCallbacks.push(() => {
setTimeout(() => {
try {
let x = onRejected(self.reason);
self.resolvePromise(promise2, x, resolve, reject);
} catch (reason) {
reject(reason);
}
}, 0);
});
}
if (self.state === FULFILLED) {
setTimeout(() => {
try {
let x = onFulfilled(self.value);
self.resolvePromise(promise2, x, resolve, reject);
} catch (reason) {
reject(reason);
}
}, 0);
}
if (self.state === REJECTED) {
setTimeout(() => {
try {
let x = onRejected(self.reason);
self.resolvePromise(promise2, x, resolve, reject);
} catch (reason) {
reject(reason);
}
})
}
});
return promise2;
}
resolvePromise(promise2, x, resolve, reject) {
let self = this;
let called = false; // called 防止多次调用
//因为promise2是上一个promise.then后的返回结果,所以如果相同,会导致下面的.then会是同一个promise2,一直都是,没有尽头
//相当于promise.then之后return了自己,因为then会等待return后的promise,导致自己等待自己,一直处于等待
if (promise2 === x) {
return reject(new TypeError('循环引用'));
}
//如果x不是null,是对象或者方法
if (x !== null && (Object.prototype.toString.call(x) === '[object Object]' || Object.prototype.toString.call(x) === '[object Function]')) {
// x是对象或者函数
try {
let then = x.then;
if (typeof then === 'function') {
then.call(x, (y) => {
// 别人的Promise的then方法可能设置了getter等,使用called防止多次调用then方法
if (called) return;
called = true;
// 成功值y有可能还是promise或者是具有then方法等,再次resolvePromise,直到成功值为基本类型或者非thenable
self.resolvePromise(promise2, y, resolve, reject);
}, (reason) => {
if (called) return;
called = true;
reject(reason);
});
} else {
if (called) return;
called = true;
resolve(x);
}
} catch (reason) {
if (called) return;
called = true;
reject(reason);
}
} else {
// x是普通值,直接resolve
resolve(x);
}
}
//catch方法
catch (onRejected) {
return this.then(null, onRejected)
} finally(fn) {
return this.then(value => {
fn();
return value;
}, reason => {
fn();
throw reason;
});
};
}
const mp1 = MyPromise.resolve(1);
const mp2 = MyPromise.resolve(2);
const mp3 = MyPromise.resolve(3);
const mp4 = MyPromise.reject(4);
MyPromise.all([mp1, mp2, mp3]).then(x => {
console.log(x);
}, (err) => {
console.log('err1', err);
})
MyPromise.race([mp1, mp4, mp2, mp3]).then(x => {
console.log(x);
}, (err) => {
console.log('err2', err);
})
var mp = new MyPromise((resolve, reject) => {
console.log(11111);
setTimeout(() => {
resolve(22222);
console.log(3333);
}, 1000);
});
mp.then(x => {
console.log(x);
}, (err) => {
console.log('err2', err);
})