实现可暂停异步任务队列的3种方式

需求：在爬取网页的时候需要同时向多个分页进行爬取，并能够进行爬取中间暂停。

let builder = x => async () => Promise.resolve(x);
let tasks = Array.from({ length:1120 }).map((_, k) => builder(`console.log(${k})`))
let index = 0;
let timer;
let canRun = true;
function run(){
    index++;
     timer = setTimeout(async () => {
        let funcSource = await tasks[index](index);
        let func = new Function(funcSource);
        func()
        if (canRun) {
            run()
        }else{
            clearTimeout(timer)
        }
    })
}
run()
setTimeout(function () {
    console.log("change canRun")
    canRun = false;
}, 10)

function sleep(milliSeconds) {
    var startTime = new Date().getTime();
    while (new Date().getTime() < startTime + milliSeconds);
};
const getRandom = async () => {
    sleep(300)
    return Math.random() > 0.1;
}
let builder = x => async () => Promise.resolve(x);
let tasks = Array.from({
    length: 1120
}).map((_, k) => builder(`console.log(${k})`))
async function run() {
    for (let task of tasks) {
        let random = await getRandom()
        if (random) {
            let source = await task();
            (new Function(source))()
        }else{
            break;
        }
    }
}
run()

const EventEmitter = require('events');
let builder = x => async () => Promise.resolve(x);
let tasks = Array.from({ length:1120 }).map((_, k) => builder(`console.log(${k})`))
function sleep(milliSeconds) {
    var startTime = new Date().getTime();
    while (new Date().getTime() < startTime + milliSeconds);
 };
const getRandom = async () => {
    sleep(300)
    return Math.random() > 0.1;
}
class Queue extends EventEmitter {
  constructor() {
    super();
    this._index = 0;
    this._start();
  }
  _start() {
    this._timer = setTimeout(async () => {
      const source = await tasks[this._index]()
      this.emit('next', source);
      this._index++;
      this._start();
    }, 0);
  }
  _stop(){
    clearTimeout(this._timer)
  }
};
let q = new Queue();
q.on('next', async (source) => {
  (new Function(source))()
});
setTimeout(()=>{
    q._stop()
}, 100)