What is a closure in JavaScript?

What is a closure in JavaScript?

• A. A closure is a function that returns another function.
• B. A closure is an array method.
• C. A closure is the global execution context.
• D. A closure is a function that retains access to its lexical scope even when executed outside that scope.

Answer: (D)

Closures happen when a function is created inside another function and the inner function keeps access to the outer function’s variables, even after the outer function has finished running. This means you can later invoke the inner function and it will still “remember” the environment in which it was created. For example: function makeCounter() { let count = 0; return function() { count++; return count; }; } const counter = makeCounter(); console.log(counter()); // 1 console.log(counter()); // 2 Here, the inner function retains access to count because it was defined within the outer function’s scope. The language’s lexical scoping and the closure mechanism ensure that the environment (the binding of count) is preserved for the inner function to use whenever it’s called. This concept explains why closures are powerful for creating private state and function factories. It’s not just about a function returning another function, it’s about preserving access to the defining scope. It isn’t an array method, nor the global execution context.

Closures happen when a function is created inside another function and the inner function keeps access to the outer function’s variables, even after the outer function has finished running. This means you can later invoke the inner function and it will still “remember” the environment in which it was created.

For example:

function makeCounter() {

let count = 0;

return function() {

count++;

return count;

};

}

const counter = makeCounter();

console.log(counter()); // 1

console.log(counter()); // 2

Here, the inner function retains access to count because it was defined within the outer function’s scope. The language’s lexical scoping and the closure mechanism ensure that the environment (the binding of count) is preserved for the inner function to use whenever it’s called.

This concept explains why closures are powerful for creating private state and function factories. It’s not just about a function returning another function, it’s about preserving access to the defining scope. It isn’t an array method, nor the global execution context.