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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

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  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.

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