Web worker

A web worker, as defined by the World Wide Web Consortium (W3C) and the Web Hypertext Application Technology Working Group (WHATWG), is a JavaScript script executed from an HTML page that runs in the background, independently of other user-interface scripts that may also have been executed from the same HTML page. Web workers are able to utilize multi-core CPUs more effectively.

The W3C and WHATWG envision web workers as long-running scripts that are not interrupted by user-interface scripts (scripts that respond to clicks or other user interactions). Keeping such workers from being interrupted by user activities should allow Web pages to remain responsive at the same time as they are running long tasks in the background.

The simplest use of workers is for performing a computationally expensive task without interrupting the user interface.

The W3C and the WHATWG are currently in the process of developing a definition for an API for web workers.

Overview

As envisioned by WHATWG, web workers are relatively heavy-weight. They are expected to be long-lived, have a high start-up performance cost, and a high per-instance memory cost.