Multithreaded Javascript

Chapter 2. Browsers

JavaScript doesn’t have a single, bespoke implementation like most other programming languages do. For example, with Python, you’re probably going to run the Python binary provided by the language maintainers. JavaScript, on the other hand, has many different implementations. This includes the JavaScript engine that ships with different web browsers, such as V8 in Chrome, SpiderMonkey in Firefox, and JavaScriptCore in Safari. The V8 engine is also used by Node.js on the server.

These separate implementations each start off by implementing some facsimile of the ECMAScript specification. As the compatibility charts that we so often need to consult suggest, not every engine implements JavaScript the same way. Certainly, browser vendors attempt to implement JavaScript features in the same manner, but bugs do happen. At the language level, there are some concurrency primitives that have been made available, which are covered in more detail in Chapters 4 and 5.

Other APIs are also added in each implementation to make the JavaScript that can be run even more powerful. This chapter focuses entirely on the multithreaded APIs that are provided by modern web browsers, the most approachable of which is the web worker.

Using these worker threads is beneficial for many reasons, but one that is particularly applicable to browsers is that, by offloading CPU-intensive work to a separate thread, the main thread is then able to dedicate more resources to rendering the UI. This ...