Queues async actions so they occur one after another

async-serial-queue.ts

// class version
class Queue {
  private p: Promise<any> = Promise.resolve();

  push<T = any>(fn: () => Promise<any>): Promise<T> {
    this.p = this.p
      .then(() => fn())
      .catch(err => {
        console.error(err);
        return fn(); //keep going to next queued
      });
    return this.p;
  }
}

// function version
function makeQueue() {
  let p: Promise<any> = Promise.resolve();
  return function queue(fn) {
    p = p.then(() => fn())
      .catch(err => {
        console.error(err);
        return fn(); //keep going to next queued
      });
    return p;
  };
}

       
// implement it ....
       
function sleep(val, dur) {
  return new Promise(res => {
    setTimeout(() => { res(val) }, dur);
  });
}

let q = new Queue()
q.push(() => sleep(1, 1000)).then(console.log)
q.push(() => sleep(2, 500)).then(console.log)
q.push(() => sleep(3, 1)).then(console.log)
       
       
let q2 = makeQueue();
q2(() => sleep(1, 1000)).then(console.log)
q2(() => sleep(2, 500)).then(console.log)
q2(() => sleep(3, 1)).then(console.log)