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---
title: "Scope - Glossary | MDN"
chunk: 1/3
source: "https://developer.mozilla.org/en-US/docs/Glossary/Scope"
category: "reference"
tags: "web, html, css, javascript, documentation"
date_saved: "2026-05-05T05:44:31.348506+00:00"
instance: "kb-cron"
---
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1. [Glossary](https://developer.mozilla.org/en-US/docs/Glossary)
2. [Scope](https://developer.mozilla.org/en-US/docs/Glossary/Scope)
# Scope
The **scope** is the current context of execution in which [values](https://developer.mozilla.org/en-US/docs/Glossary/Value) and expressions are "visible" or can be referenced. If a [variable](https://developer.mozilla.org/en-US/docs/Glossary/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](https://developer.mozilla.org/en-US/docs/Glossary/Function).
In addition, identifiers declared with certain syntaxes, including [`let`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/let), [`const`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/const), [`class`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/class), or (in strict mode) [`function`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/function), can belong to an additional scope:
* Block scope: The scope created with a pair of curly braces (a [block](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/block)).
A [function](https://developer.mozilla.org/en-US/docs/Glossary/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](https://developer.mozilla.org/en-US/docs/Glossary/Scope#see_also)
## [See also](https://developer.mozilla.org/en-US/docs/Glossary/Scope#see_also)
* [Scope (computer science)](https://en.wikipedia.org/wiki/Scope_\(computer_science\)) on Wikipedia
* [Block scoping rules](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/block#block_scoping_rules_with_let_const_class_or_function_declaration_in_strict_mode)
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