The area in your code where a variable is accessible — where it "exists."
Scope determines where in your code a variable can be accessed. A variable declared inside a function is only available inside that function (function scope). A variable declared inside an if block with let or const is only available inside that block (block scope).
There are three main scopes in JavaScript: global scope (accessible everywhere), function scope (inside the function), and block scope (inside curly braces with let/const). The var keyword ignores block scope, which is why modern JavaScript prefers let and const.
Understanding scope prevents bugs like accidentally overwriting variables or accessing undefined values. In React, components have their own scope — variables in one component don't leak into another.
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