---
title: "JavaScript engine - Glossary | MDN"
chunk: 1/3
source: "https://developer.mozilla.org/en-US/docs/Glossary/Engine/JavaScript"
category: "reference"
tags: "web, html, css, javascript, documentation"
date_saved: "2026-05-05T05:30:34.484052+00:00"
instance: "kb-cron"
---

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HTML
[HTML: Markup language](https://developer.mozilla.org/en-US/docs/Web/HTML) 

HTML reference
    
  * [Elements](https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/Elements)
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CSS
[CSS: Styling language](https://developer.mozilla.org/en-US/docs/Web/CSS) 

CSS reference
    
  * [Properties](https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Properties)
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  * [Colors](https://developer.mozilla.org/en-US/docs/Web/CSS/Guides/Colors/Applying_color)
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Layout cookbook
    
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JavaScriptJS
[JavaScript: Scripting language](https://developer.mozilla.org/en-US/docs/Web/JavaScript) 

JS reference
    
  * [Standard built-in objects](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects)
  * [Expressions & operators](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators)
  * [Statements & declarations](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements)
  * [Functions](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions)
  * [See all…](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference "See all JavaScript references")

JS guides
    
  * [Control flow & error handing](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Control_flow_and_error_handling)
  * [Loops and iteration](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Loops_and_iteration)
  * [Working with objects](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Working_with_objects)
  * [Using classes](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Using_classes)
  * [See all…](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide "See all JavaScript guides")

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[Web APIs: Programming interfaces](https://developer.mozilla.org/en-US/docs/Web/API) 

Web API reference
    
  * [File system API](https://developer.mozilla.org/en-US/docs/Web/API/File_System_API)
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  * [See all…](https://developer.mozilla.org/en-US/docs/Web/API "See all Web API guides")

Web API guides
    
  * [Using the Web animation API](https://developer.mozilla.org/en-US/docs/Web/API/Web_Animations_API/Using_the_Web_Animations_API)
  * [Using the Fetch API](https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API/Using_Fetch)
  * [Working with the History API](https://developer.mozilla.org/en-US/docs/Web/API/History_API/Working_with_the_History_API)
  * [Using the Web speech API](https://developer.mozilla.org/en-US/docs/Web/API/Web_Speech_API/Using_the_Web_Speech_API)
  * [Using web workers](https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API/Using_web_workers)

All
[All web technology](https://developer.mozilla.org/en-US/docs/Web) 

Technologies
    
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Topics
    
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Learn
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Frontend developer course
    
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Learn HTML
    
  * [Structuring content with HTML module](https://developer.mozilla.org/en-US/docs/Learn_web_development/Core/Structuring_content)

Learn CSS
    
  * [CSS styling basics module](https://developer.mozilla.org/en-US/docs/Learn_web_development/Core/Styling_basics)
  * [CSS layout module](https://developer.mozilla.org/en-US/docs/Learn_web_development/Core/CSS_layout)

Learn JavaScript
    
  * [Dynamic scripting with JavaScript module](https://developer.mozilla.org/en-US/docs/Learn_web_development/Core/Scripting)

Tools
Discover our tools 
  * [Playground](https://developer.mozilla.org/en-US/play)
  * [HTTP Observatory](https://developer.mozilla.org/en-US/observatory)

  * [Border-image generator](https://developer.mozilla.org/en-US/docs/Web/CSS/Guides/Backgrounds_and_borders/Border-image_generator)
  * [Border-radius generator](https://developer.mozilla.org/en-US/docs/Web/CSS/Guides/Backgrounds_and_borders/Border-radius_generator)
  * [Box-shadow generator](https://developer.mozilla.org/en-US/docs/Web/CSS/Guides/Backgrounds_and_borders/Box-shadow_generator)
  * [Color format converter](https://developer.mozilla.org/en-US/docs/Web/CSS/Guides/Colors/Color_format_converter)
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[Blog](https://developer.mozilla.org/en-US/blog/)
  1. [Glossary](https://developer.mozilla.org/en-US/docs/Glossary)
  2. [Engine](https://developer.mozilla.org/en-US/docs/Glossary/Engine)
  3. [JavaScript engine](https://developer.mozilla.org/en-US/docs/Glossary/Engine/JavaScript)

# JavaScript engine
**JavaScript engines** are interpreters that parse and execute [JavaScript](https://developer.mozilla.org/en-US/docs/Glossary/JavaScript) 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 web [browsers](https://developer.mozilla.org/en-US/docs/Glossary/Browser) to run client-side code but can also be used in server-side environments like [Node.js](https://developer.mozilla.org/en-US/docs/Glossary/Node.js).
In a browser, the JavaScript engine operates together with the rendering engine via the [Document Object Model](https://developer.mozilla.org/en-US/docs/Glossary/DOM) and [Web IDL](https://developer.mozilla.org/en-US/docs/Glossary/WebIDL) bindings. Some JavaScript engines also execute [WebAssembly](https://developer.mozilla.org/en-US/docs/Glossary/WebAssembly) code in the same sandbox as regular JavaScript code.
Do not confuse JavaScript engines with [rendering engines](https://developer.mozilla.org/en-US/docs/Glossary/Engine/Rendering), which are also crucial parts of browsers.
Common JavaScript engines include:
  * [V8](https://v8.dev/)
  * [SpiderMonkey](https://spidermonkey.dev/)
  * [JavaScriptCore](https://developer.apple.com/documentation/javascriptcore)

## In this article
  * [See also](https://developer.mozilla.org/en-US/docs/Glossary/Engine/JavaScript#see_also)

##  [See also](https://developer.mozilla.org/en-US/docs/Glossary/Engine/JavaScript#see_also)
  * [JavaScript engine](https://en.wikipedia.org/wiki/JavaScript_engine) on Wikipedia
  * [JavaScript implementations](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/JavaScript_technologies_overview#javascript_implementations)
  * Related glossary terms: 
    * [Engine](https://developer.mozilla.org/en-US/docs/Glossary/Engine)
    * [JavaScript](https://developer.mozilla.org/en-US/docs/Glossary/JavaScript)
    * [WebAssembly](https://developer.mozilla.org/en-US/docs/Glossary/WebAssembly)
    * [Browser](https://developer.mozilla.org/en-US/docs/Glossary/Browser)
    * [Node.js](https://developer.mozilla.org/en-US/docs/Glossary/Node.js)