promise簡易版

class Promises {

constructor( cb) {

this. thenArr = []; //存放then函數裏面的成功的函數和失敗的函數

this. cb = cb; //promise中的回調函數

this. count = 0; //計數

this. returnText = null; //返回值

this. resolve = this. resolve. bind( this);

this. reject = this. reject. bind( this);

this. cb( this. resolve, this. reject);

}

static all( promiseData) {

let resultData = [];

let errData = [];

return new Promises(( res, rej) => {

promiseData. forEach( i => {

i. then( data => {

resultData. push( data);

test();

}, ( err) => {

errData. push( err);

testerr();

})

})

function test() {

if ( promiseData. length === resultData. length) {

res( resultData)

}

}

 

function testerr() {

if ( errData. length > 0) {

rej( errData[ 0])

}

}

})

}

static race( promiseData) {

let resultData = [];

let errData = [];

return new Promises(( res, rej) => {

promiseData. forEach( i => {

i. then( data => {

resultData. push( data);

test();

}, ( err) => {

errData. push( err);

testerr();

})

})

function test() {

if ( promiseData. length > resultData. length) {

res( resultData)

}

}

function testerr() {

if ( errData. length === errData. length) {

rej( errData[ 0])

}

}

})

}

resolve( data) {

// 判斷返回值的狀態

// 1.返回值是promise

//2.返回值是普通的

let rest = this. thenArr. slice( this. count)

if ( this. returnText && this. returnText instanceof Promises) {

rest. forEach( item => {

this. returnText. then( item. okCb, item. errCn);

})

return;

} else if( this. returnText) {

this. thenArr[ this. count]. okCb( this. returnText);

} else {

this. returnText = this. thenArr[ this. count]. okCb( data);

}

this. count++;

if ( this. count < this. thenArr. length) {

this. resolve( data);

}

}

reject( err){

//若是失敗，根據count執行當前then函數的失敗函數

this. thenArr[ this. count]. errCn( err)

//若是失敗的then函數下面還有未執行的then函數，則直接調用下一個then函數的成功函數

this. count++

if( this. count< this. thenArr. length){

this. resolve()

}

}

then( okCb, errCn) {

this. thenArr. push({

okCb,

errCn

})

return this;

}

}

let pro1=() =>{

return new Promises(( resolve, reject) =>{

setTimeout(() =>{

reject( 1)

}, 1000)

})

}

let pro2=() =>{

return new Promises(( resolve, reject) =>{

setTimeout(() =>{

reject( 2)

}, 2000)

})

}

Promises. race([ pro1(), pro2()]). then(( data) =>{

console. log( data)

},( err) =>{

console. log( err+ "2344")

})

// new Promises((res, rej) => {

// setTimeout(() => {

// rej(123)

// }, 1000)

// }).then((data) => {

// console.log(data)

// }, (err) => {

// console.log('err', err)

// }).then((data) => {

// return new Promise((res, rej) => {

// res(456)

// })

// }).then((data) => {

// console.log(data)

// })