butterfly/kb
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity
e206bfafb2
kb/data/developer.mozilla.org/en-US/docs/Glossary/Scope-0.md

11 KiB
Raw Blame History

title chunk source category tags date_saved instance
Scope - Glossary | MDN 1/3 https://developer.mozilla.org/en-US/docs/Glossary/Scope reference web, html, css, javascript, documentation 2026-05-05T05:44:31.348506+00:00 kb-cron

MDN HTML HTML: Markup language

HTML reference

HTML guides

Markup languages

CSS CSS: Styling language

CSS reference

CSS guides

Layout cookbook

JavaScriptJS JavaScript: Scripting language

JS reference

JS guides

Web APIs Web APIs: Programming interfaces

Web API reference

Web API guides

All All web technology

Technologies

Topics

Learn Learn web development

Frontend developer course

Learn HTML

Learn CSS

Learn JavaScript

Tools Discover our tools

About Get to know MDN better

Blog

  1. Glossary
  2. Scope

Scope

The scope is the current context of execution in which values and expressions are "visible" or can be referenced. If a variable or expression is not in the current scope, it will not be available for use. Scopes can also be layered in a hierarchy, so that child scopes have access to parent scopes, but not vice versa. JavaScript has the following kinds of scopes:

  • Global scope: The default scope for all code running in script mode.
  • Module scope: The scope for code running in module mode.
  • Function scope: The scope created with a function.

In addition, identifiers declared with certain syntaxes, including let, const, class, or (in strict mode) function, can belong to an additional scope:

  • Block scope: The scope created with a pair of curly braces (a block).

A function creates a scope, so that (for example) a variable defined exclusively within the function cannot be accessed from outside the function or within other functions. For instance, the following is invalid: However, the following code is valid due to the variable being declared outside the function, making it global: Blocks only scope let and const declarations, but not var declarations.

In this article

See also