异步任务调度器

[CongratulateWE]

参考：

class Scheduler {
    constructor(limit) {
        this.limit = limit
        this.number = 0
        this.queue = []
    }
    addTask(timeout, str) {
        this.queue.push([timeout, str])
    }
    start() {
        if (this.number < this.limit&&this.queue.length) {
            var [timeout, str] = this.queue.shift()
            this.number++
            setTimeout(() => {
                console.log(str)
                this.number--
                this.start()
            }, timeout * 1000);
            this.start()
        }
    }
}