promise.consecutively

When you need to chain many promises and that the order of completion matters.

Scenario

Let's say you have an unknown list of promises that need to resolve in order. You want promise3 to be fired only after promise2 has successfully resolved, and promise2 to be fired only after promise1 has successfully resolved.

When these promises are well-known in advance you can chain them like this :

promise1.then(() => promise2).then(() => promise3);

In the scenario where these promises are a dynamic list and their total number cannot be known in advance you can use the consecutively.iterate function to iterate over a list.

consecutively.iterate([promise_1, promise_2, promise_3, ...., promise_n], callBackFn).then(()=>{})

Demo

See the demo on stackblitz

How to use in Javascript

In this example, we have three promises that takes some seconds to resolve. I passed also the console.info function as callback to display the resolved response of each promises.

var promiseConsecutively = require('promise.consecutively').consecutively;

promiseConsecutively
  .iterate(
    [
      new Promise((resolve, reject) => {
        setTimeout(() => {
          resolve('number one - ' + new Date());
        }, 1000);
      }),
      new Promise((resolve, reject) => {
        setTimeout(() => {
          resolve('number two - ' + new Date());
        }, 5000);
      }),
      new Promise((resolve, reject) => {
        setTimeout(() => {
          resolve('number three - ' + new Date());
        }, 10000);
      })
    ],
    console.info
  )
  .then((result) => console.log('results', result));

The output is the following :

'number one - Thu Dec 03 2020 15:02:54 GMT+0100 (Central European Standard Time)';

'number two - Thu Dec 03 2020 15:02:58 GMT+0100 (Central European Standard Time)';

'number three - Thu Dec 03 2020 15:03:03 GMT+0100 (Central European Standard Time)';

'results'[
  'number one - Thu Dec 03 2020 15:02:54 GMT+0100 (Central European Standard Time)',
  'number two - Thu Dec 03 2020 15:02:58 GMT+0100 (Central European Standard Time)',
  'number three - Thu Dec 03 2020 15:03:03 GMT+0100 (Central European Standard Time)'
];

How to use in Typescript

import { consecutively } from "promise.consecutively";

interface TestInterface {
  i_attr: string;
}

const p1: Promise<TestInterface> = new Promise<TestInterface>(
  (resolver, _reject) => {
    resolver({ i_attr: "number 1" });
  }
);
const p2: Promise<TestInterface> = new Promise<TestInterface>(
  (resolver, _reject) => {
    resolver({ i_attr: "number 2" });
  }
);
const p3: Promise<TestInterface> = new Promise<TestInterface>(
  (resolver, _reject) => {
    resolver({ i_attr: "number 3" });
  }
);

consecutively
  .iterate<TestInterface>([p1, p2, p3], console.log)
  .then((response) => {
    console.log(response);
  });