Q37. JS实现一个带并发限制的异步调度器Scheduler

[lstoryc]

class Scheduler {
	constructor(count) {
		this.count = 2
		this.queue = []
		this.run = []
	}

	add(task) {
		this.queue.push(task)
		return this.schedule()
	}

	schedule() {
		if (this.run.length < this.count && this.queue.length) {
		  	const task = this.queue.shift()
		  	const promise = task().then(() => {
		  		this.run.splice(this.run.indexOf(promise), 1)
		  	})
		  	this.run.push(promise)
		  	return promise
		} else {
		  	return Promise.race(this.run).then(() => this.schedule())
		}
	}
}