Answer 1

A closure is a function that has access to variables from its outer scope, captured at the time the function was created. This is a fundamental JavaScript concept because functions are first-class and lexical scoping is how JavaScript resolves variable names. Practical example — a configurable multiplier: function createMultiplier(factor) { return function(number) { return number * factor; }; } const double = createMultiplier(2); const triple = createMultiplier(3); console.log(double(5)); // 10 console.log(triple(5)); // 15 factor is captured in the closure at creation time. double and triple each have their own closed-over factor value. This pattern is called partial application and is the basis for currying in functional programming.