JavaScript engines are interpreters that parse and executeJavaScript code. Modern JavaScript engines use just-in-time (JIT) compilation to convert JavaScript code into machine code that can be executed by a computer's processor. A JavaScript engine is typically developed and used in webbrowsers to run client-side code but can also be used in server-side environments likeNode.js.

In a browser, the JavaScript engine operates together with the rendering engine via theDocument Object Model andWeb IDL bindings. Some JavaScript engines also executeWebAssembly code in the same sandbox as regular JavaScript code.

Do not confuse JavaScript engines withrendering engines, which are also crucial parts of browsers.

Common JavaScript engines include:

• V8
• SpiderMonkey
• JavaScriptCore

This page was last modified onJul 11, 2025 byMDN contributors.