JavaScript with Promises

Chapter 4. Using Libraries and Frameworks

Before the ES6 Promise API existed, many JavaScript libraries and frameworks implemented their own version of Promises. Some libraries were written for the sole purpose of providing promises while established libraries like jQuery added them to handle their async APIs.

Promise libraries can act as polyfills in older web browsers and other environments where native promises are not provided. They can also supplement the standard API with a wide set of functions for managing promises. If your code only uses promises that you create you’re in a good position to choose a library and take full advantage of its extended API. And if you are handling promises that other libraries produced, you can wrap those promises with ones from your chosen library to access the additional features.

This chapter focuses on nonnative promise implementations. The majority of the chapter covers Bluebird, a fast and robust promise library. Although Bluebird is a compelling choice, there are other good options. For example, the Q promise library predates Bluebird and is widely used in applications and frameworks including AngularJS. Q and other libraries are not discussed in detail because this chapter is not a guide to choosing between libraries. It is an introduction to the enhancements that third-party libraries offer to demonstrate their value. The Promise implementation in jQuery is also discussed because of jQuery’s immense popularity. However, this is not ...