A closure is a function that retains access to its outer scope's variables even after the outer scope has finished execution.
Closures are useful in JavaScript for creating private variables and methods, as they provide a way to encapsulate state within a function.
They are commonly used in event handlers and callbacks, where they allow functions to maintain access to their original context.
Closures are created every time a function is defined in another function, and they have access to the variables of the outer function even after the outer function has returned.
This makes closures useful for tasks such as data hiding, memoization, and creating factory functions.
Overall, closures are a powerful feature of JavaScript that allow for more flexible and maintainable code.