Handwritten promise series - all

Handwritten questions are indispensable during the interview , and promise Related handwritten questions are often asked , Let's tidy up here promise Handwriting series .
The entire series is expected to have handwritten articles for the following functions , Let's start today all function

• all
• any
• race
• allSettled
• resolve+reject
• promise Handwritten implementation

Promise.all effect

Promise.all() Method is used to add more than one Promise The example is packaged into a new Promise example .

const a = Promise.all([p1, p2, p3])

Final a The status of the p1,p2,p3 decision . Only the states are fulfilled when a The state of is fulfilled, here ,p1,p2,p3 The return value of consists of an array , Pass to p Callback function for . Just one for rejected,a The state of will become rejected, At this time, the first was rejectd The return value of the strength of will be passed to a Callback function for . If the array passed in is not promise Instance value or object , Will be encapsulated as a state of fulfilled State of promise, The return value is itself .

Combined with the above characteristics , Let's write a few examples , Test it Promise.all Results in various cases

let promise1 = new Promise((resolve, reject) => {
    
    setTimeout(() => {
    
        console.log('promise1')
        resolve(1)
    }, 2000)
})

let promise2 = new Promise((resolve, reject) => {
    
    setTimeout(() => {
    
        console.log('promise2')
        resolve(2)
    }, 1000)
})

let promise3 = new Promise((resolve, reject) => {
    
    setTimeout(() => {
    
        console.log('promise2')
        reject('error')
    }, 3000)
})
let b = Promise.all([promise1, promise2, {
    a: 2}, promise3])
console.log(b) // The direct output is peding State of Promise

//  Output after three seconds 
console.log(b)
/** Promise {<rejected>: 'error'} [[Prototype]]: Promise [[PromiseState]]: "rejected" [[PromiseResult]]: "error" */
let c = Promise.all([promise1, promise2, {
    a: 2}])
console.log(c)
/** Promise {<fulfilled>: Array(3)} [[Prototype]]: Promise [[PromiseState]]: "fulfilled" [[PromiseResult]]: Array(3) 0: 1 1: 2 2: {a: 2} length: 3 [[Prototype]]: Array(0) */

Handwritten implementation Promise.all

Promise.myAll = (promises) => {
    
	return new Promise((resolve, reject) => {
    
		let result = []
		promises.forEach((promise, i) => {
    
			//  Will all not promise The object is encapsulated as fulfilled State of promise object , about promise Objects are not processed 
			Promise.resolve(promise).then((res) => {
    
				result[i] = res
				if(i === promises.length - 1){
    
					resolve(result)
				}
			}).catch((err) => {
    
				reject(err)
			})
		})
	})
}

let b = Promise.myAll([promise1, promise2, {
    a: 2}, promise3])
let c = Promise.myAll([promise1, promise2, {
    a: 2}])
console.log(b)
console.log(c)
//  Results and all The same function