chaining async method calls - javascript

Question

You have a prototype object Foo with two async method calls, bar and baz.

var bob = new Foo()

Foo.prototype.bar = function land(callback) {
  setTimeout(fun         


        

Answer 1

Warning this isn't quite right yet. Ideally we'd subclass Promise and have proper then/catch functionality but there are some caveats with subclassing bluebird Promise. The idea is to store an internal array of promise generating functions, then when a Promise is waited on (then/await) serially wait on those promises.

const Promise = require('bluebird');

class Foo {
  constructor() {
    this.queue = [];
  }

  // promise generating function simply returns called pGen
  pFunc(i,pGen) {
    return pGen();
  }

  bar() {
    const _bar = () => {
      return new Promise( (resolve,reject) => {
        setTimeout( () => {
          console.log('bar',Date.now());
          resolve();
        },Math.random()*1000);
      })      
    }
    this.queue.push(_bar);
    return this;
  }

  baz() {
    const _baz = () => {
      return new Promise( (resolve,reject) => {
        setTimeout( () => {
          console.log('baz',Date.now());
          resolve();
        },Math.random()*1000);
      })      
    }
    this.queue.push(_baz);
    return this;
  }

  then(func) {
    return Promise.reduce(this.queue, this.pFunc, 0).then(func);
  }
}


const foo = new Foo();
foo.bar().baz().then( () => {
  console.log('done')
})

result:

messel@messels-MBP:~/Desktop/Dropbox/code/js/async-chain$ node index.js 
bar 1492082650917
baz 1492082651511
done