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How JavaScript Uses Lexical Environments to Manage Variable Scope

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A lexical environment is an internal structure JavaScript creates to track variables and functions within a given scope, along with a reference to any outer scope. Each time a function is called, JavaScript generates a new lexical environment containing that function's parameters and local variables. When a variable is referenced, JavaScript searches the current environment first, then moves outward through enclosing scopes until it reaches the global environment. If the variable is not found anywhere in this chain, JavaScript throws a ReferenceError. Crucially, scope in JavaScript is determined by where code is physically written — not where a function is invoked — which is what the term 'lexical' refers to.

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