自定义Promise
普通构造函数类型
function Promise(excutor) {
this.PromiseState = 'pending';
this.PromiseResult = null;
this.callbacks = [];
const self = this;
function resolve(data) {
if (self.PromiseState !== 'pending') return;
self.PromiseState = 'fulfilled';
self.PromiseResult = data;
setTimeout(() => {
self.callbacks.forEach(item => {
item.onResolved(data)
})
});
}
function reject(data) {
if (self.PromiseState !== 'pending') return;
self.PromiseState = 'rejected';
self.PromiseResult = data;
setTimeout(() => {
self.callbacks.forEach(item => {
item.onRejected(data)
})
});
}
try {
excutor(resolve, reject);
} catch (e) {
reject(e)
}
}
Promise.prototype.then = function (onResolved, onRejected) {
const self = this;
if (typeof onRejected !== 'function') {
onRejected = reason => {
throw reason
}
}
if (typeof onResolved !== 'function') {
onResolved = value => value
}
return new Promise((resolve, reject) => {
function callback(type) {
try {
let result = type(self.PromiseResult)
if (result instanceof Promise) {
result.then(v => {
resolve(v)
}, r => {
reject(r)
})
} else {
resolve(result)
}
} catch (e) {
reject(e)
}
}
if (this.PromiseState === 'fulfilled') {
setTimeout(() => {
callback(onResolved)
});
}
if (this.PromiseState === 'rejected') {
setTimeout(() => {
callback(onRejected)
});
}
if (this.PromiseState === 'pending') {
this.callbacks.push({
onResolved: function () {
callback(onResolved)
},
onRejected: function () {
callback(onRejected)
}
})
}
})
}
Promise.prototype.catch = function (onRejected) {
return this.then(undefined, onRejected);
}
Promise.resolve = function (value) {
return new Promise((resolve, reject) => {
if (value instanceof Promise) {
value.then(v => {
resolve(v)
}, r => {
reject(r)
})
} else {
resolve(value)
}
})
}
Promise.reject = function (reason) {
return new Promise((resolve, reject) => {
reject(reason)
})
}
Promise.all = function (promises) {
return new Promise((resolve, reject) => {
let count = 0;
let arr = [];
for (let i = 0; i < promises.length; i++) {
promises[i].then(v => {
count++;
arr[i] = v;
if (count === promises.length) {
resolve(arr)
}
}, r => {
reject(r)
})
}
})
}
Promise.race = function(promises){
return new Promise((resolve,reject)=>{
for (let i = 0; i < promises.length; i++) {
promises[i].then(v=>{
resolve(v)
},r=>{
reject(r)
})
}
})
}
ES6 Class 类型
class Promise {
constructor(excutor) {
this.PromiseState = 'pending';
this.PromiseResult = null;
this.callbacks = [];
const self = this;
function resolve(data) {
if (self.PromiseState !== 'pending') return;
self.PromiseState = 'fulfilled';
self.PromiseResult = data;
setTimeout(() => {
self.callbacks.forEach(item => {
item.onResolved(data)
})
});
}
function reject(data) {
if (self.PromiseState !== 'pending') return;
self.PromiseState = 'rejected';
self.PromiseResult = data;
setTimeout(() => {
self.callbacks.forEach(item => {
item.onRejected(data)
})
});
}
try {
excutor(resolve, reject);
} catch (e) {
reject(e)
}
}
then(onResolved, onRejected) {
const self = this;
if (typeof onRejected !== 'function') {
onRejected = reason => {
throw reason
}
}
if (typeof onResolved !== 'function') {
onResolved = value => value
}
return new Promise((resolve, reject) => {
function callback(type) {
try {
let result = type(self.PromiseResult)
if (result instanceof Promise) {
result.then(v => {
resolve(v)
}, r => {
reject(r)
})
} else {
resolve(result)
}
} catch (e) {
reject(e)
}
}
if (this.PromiseState === 'fulfilled') {
setTimeout(() => {
callback(onResolved)
});
}
if (this.PromiseState === 'rejected') {
setTimeout(() => {
callback(onRejected)
});
}
if (this.PromiseState === 'pending') {
this.callbacks.push({
onResolved: function () {
callback(onResolved)
},
onRejected: function () {
callback(onRejected)
}
})
}
})
}
catch(onRejected) {
return this.then(undefined, onRejected);
}
static resolve(value) {
return new Promise((resolve, reject) => {
if (value instanceof Promise) {
value.then(v => {
resolve(v)
}, r => {
reject(r)
})
} else {
resolve(value)
}
})
}
static reject(reason) {
return new Promise((resolve, reject) => {
reject(reason)
})
}
static all(promises) {
return new Promise((resolve, reject) => {
let count = 0;
let arr = [];
for (let i = 0; i < promises.length; i++) {
promises[i].then(v => {
count++;
arr[i] = v;
if (count === promises.length) {
resolve(arr)
}
}, r => {
reject(r)
})
}
})
}
static race(promises) {
return new Promise((resolve, reject) => {
for (let i = 0; i < promises.length; i++) {
promises[i].then(v => {
resolve(v)
}, r => {
reject(r)
})
}
})
}
}