Mastering JavaScript Design Patterns - Second Edition

Doing two things at once – multithreading

Doing two things at once is hard. For many years the solution in the computer world was to use either multiple processes or multiple threads. The difference between the two is fuzzy due to implementation differences on different operating systems but threads are typically lighter-weight versions of processes. JavaScript on the browser supports neither of these approaches.

Historically, there has been no real need for multithreading on a browser. JavaScript was used to manipulate the user interface. When manipulating a UI, even in other languages and windowing environments, only one thread is permitted to act at a time. This avoids race conditions that would be very obvious to users.

However, as JavaScript ...