Introduction to Asynchronous Language Features

JavaScript’s single-threaded and asynchronous nature

The JavaScript runtime, whether it is running in the browser or whether it is running on a server through Node, is single-threaded. This means that one, and only one, piece of code will be running at a particular time. This code runs in what is known as the main thread.

JavaScript has also been built around an asynchronous approach, meaning that the main thread will not pause when requested to load a resource of some sort.

It will, instead, place this request onto an internal queue, which will eventually be processed at a later point in time. While the single-threadedness of JavaScript may take a while to get your head around, it does take away the need for in-memory locking mechanisms, as are used in other languages to handle multiple threads of execution.

This makes the JavaScript runtime a little easier to understand and to work with.