SOURCE

function timeout(time) {
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            resolve()
        }, time)
    })
}

class SuperTask {
    constructor(parallelCount = 2) {
        this.parallelCount = parallelCount
        this.tasks = []
        this.runningCount = 0
    }
    add(task) {
        return new Promise((resolve, reject) => {
            this.tasks.push({ task, resolve, reject })
            this._run()
        })
    }
    _run() {
        while ((this.runningCount < this.parallelCount) && this.tasks.length) {
            const { task, resolve, reject } = this.tasks.shift()
            this.runningCount++
            Promise.resolve(task())
                .then(resolve, reject)
                .finally(() => {
                    this.runningCount--
                    this._run()
                })
        }
    }
}

const superTask = new SuperTask()
function addTask(time, name) {
    superTask
        .add(() => timeout(time))
        .then(() => {
            console.log(`${name}任务完成`)
        })
}
addTask(1000, 1)
addTask(1000, 2)
addTask(1000, 3)
addTask(1000, 4)
addTask(1000, 5)