promise-polyfill

What is promise-polyfill?

The promise-polyfill npm package is a lightweight implementation of the ES6 Promise specification. It is designed to provide a simple and efficient way to use Promises in environments that do not natively support them, such as older browsers.

What are promise-polyfill's main functionalities?

Basic Promise Usage

This code demonstrates the basic usage of a Promise. It creates a new Promise that resolves with the message 'Success!' after 1 second, and then logs the message to the console.

const Promise = require('promise-polyfill');

const promise = new Promise((resolve, reject) => {
  setTimeout(() => {
    resolve('Success!');
  }, 1000);
});

promise.then((message) => {
  console.log(message); // 'Success!'
});

Chaining Promises

This code demonstrates how to chain multiple .then() calls to handle a sequence of asynchronous operations. Each .then() call receives the resolved value from the previous Promise and returns a new value.

const Promise = require('promise-polyfill');

const promise = new Promise((resolve, reject) => {
  setTimeout(() => {
    resolve(1);
  }, 1000);
});

promise
  .then((value) => {
    console.log(value); // 1
    return value + 1;
  })
  .then((value) => {
    console.log(value); // 2
    return value + 1;
  })
  .then((value) => {
    console.log(value); // 3
  });

Handling Errors

This code demonstrates how to handle errors in Promises using the .catch() method. If the Promise is rejected, the error message is logged to the console.

const Promise = require('promise-polyfill');

const promise = new Promise((resolve, reject) => {
  setTimeout(() => {
    reject('Error occurred!');
  }, 1000);
});

promise
  .then((value) => {
    console.log(value);
  })
  .catch((error) => {
    console.error(error); // 'Error occurred!'
  });

Other packages similar to promise-polyfill

es6-promise

The es6-promise package is another polyfill for the ES6 Promise specification. It provides a similar API to promise-polyfill and is widely used in environments that lack native Promise support. Compared to promise-polyfill, es6-promise is slightly larger in size but offers more comprehensive test coverage and compatibility.

bluebird

Bluebird is a fully-featured Promise library that offers a wide range of additional features and optimizations beyond the ES6 Promise specification. It includes utilities for working with collections, cancellation, and more. While it is more powerful and feature-rich than promise-polyfill, it is also significantly larger in size.

q

Q is a popular Promise library that predates the ES6 Promise specification. It provides a rich set of features for working with asynchronous code, including support for deferred objects and advanced error handling. Q is more feature-rich than promise-polyfill but has a larger footprint and a different API.

README

# Promise [![travis][travis-image]][travis-url]

Lightweight ES6 Promise polyfill for the browser and node. Adheres closely to the spec. It is a perfect polyfill IE, Firefox or any other browser that does not support native promises.

This implementation is based on then/promise. It has been changed to use the prototype for performance and memory reasons.

For API information about Promises, please check out this article HTML5Rocks article.

It is extremely lightweight. < 1kb Gzipped

Browser Support

IE8+, Chrome, Firefox, IOS 4+, Safari 5+, Opera

Downloads

• Promise
• Promise-min

Node

npm install promise-polyfill

Bower

bower install promise-polyfill

Simple use

var prom = new Promise(function(resolve, reject) {
  // do a thing, possibly async, then…

  if (/* everything turned out fine */) {
    resolve("Stuff worked!");
  }  else {
    reject(new Error("It broke"));
  }
});

// Do something when async done
prom.then(function() {
  ...
});

Performance

By default promise-polyfill uses setImmediate, but falls back to setTimeout for executing asynchronously. If a browser does not support setImmediate (IE/Edge are the only browsers with setImmediate), you may see performance issues. Use a setImmediate polyfill to fix this issue. setAsap or setImmediate work well.

If you polyfill window.setImmediate or use Promise._setImmediateFn(immedateFn) it will be used instead of window.setTimeout

npm install setasap --save

var Promise = require('promise-polyfill');
var setAsap = require('setasap');
Promise._setImmediateFn(setAsap);

Unhandled Rejections

promise-polyfill will warn you about possibly unhandled rejections. It will show a console warning if a Promise is rejected, but no .catch is used. You can turn off this behavior by setting Promise._setUnhandledRejectionFn(<rejectError>). If you would like to disable unhandled rejections. Use a noop like below.

Promise._setUnhandledRejectionFn(function(rejectError) {});

Testing

npm install
npm test

License

MIT

Changelog

5.0.0 Removed multiple params from Promise.all

Removed non standard functionality of passing multiple params to Promise.all. You must pass an array now. You must change this code

Promise.all(prom1, prom2, prom3);

to this

Promise.all([prom1, prom2, prom3]);