In JavaScript, the scope chain is a mechanism that determines the order in which nested functions access variables from their containing scopes, enabling variable lookup from the innermost to the outermost scope. This chain ensures that functions have access to variables in their own scope as well as those in parent scopes, but not in sibling or child scopes.

Scope Chain

scope chain

Nested functions are functions defined within other functions, allowing for encapsulation and the creation of closures that can capture and remember the environment in which they were created. This technique is often used to create helper functions that are only relevant within the scope of the enclosing function, promoting modularity and reducing the potential for naming conflicts.

nested functions

variable lookup

Innermost scope

outermost scope

containing scopes

parent scopes

Sibling scopes

child scopes

JavaScript scope

Variables and Data Types

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