How do you control the number of concurrent promises you execute

Promises are often seen in asynchronous operations, handling multiple concurrent asynchronous processes. Promises themselves have promises.all () promise.allSettled () promise.race (), etc., but they do not control the number of concurrent processes. This article implements a Schedule class that can be used to control the number of concurrent requests.

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class Schedule{

    constructor(maxNum){
        this.list = [];
        this.maxNum = maxNum
        this.workingNum = 0
    }
    
    add(promiseCreator){
        this.list.push(promiseCreator)
    }

    start(){
        for (let index = 0; index < this.maxNum; index++) {
            this.doNext()
        }
    }

    doNext(){
        if(this.list.length && this.workingNum < this.maxNum){
            this.workingNum++;
            const promise = this.list.shift();
            promise().then(() = >{
                this.workingNum--;
                this.doNext(); })}}}const timeout = time= > new Promise((resolve) = >{
    setTimeout(resolve, time)
}) 

const schedule = new Schedule(2);

const addTask = (time, order) = >{
    schedule.add(() = >timeout(time).then(() = >{
        console.log(order);
    }))
}

addTask(1000.1)
addTask(500.2)
addTask(300.3)
addTask(400.4)

schedule.start()

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The execution result