Promises were one of the most exciting novelties of ES6. You might have used Promises before with libraries like Bluebird or Q, but they only became a standard JavaScript feature in 2015.

The Promise object represents the eventual completion (or failure) of an asynchronous operation, and its resulting value.

A Promise does something that can take some time, but eventually it will resolve if everything went well or reject if something went wrong. With _.then _and .catch you can then do something respectively with the result or with the error.

const promise = new Promise(function(resolve, reject) {
	  setTimeout(() => {
	      if (Math.random(1) > 0.5) {
	        resolve('Some value');
	      } else {
	        reject('Some error');
	      }
	  }, 500);
	});

	promise.then((response) => {
	  console.log(response);
	}).catch(err => {
	  console.log(err);
	});

They were introduced almost five years ago, so Promises shouldn’t be anything new to you, but ES2020 comes with a new feature: Promise.allSettled. It comes to fill a gap left by the ES6 Promise.all and Promise.race.

This tutorial covers Promise.allSettled functionality introduced in ES2020. Also, Promise.all has been compared with Promise.allSettled in this tutorial.

#es2020 #javascript #programming