Which statement about JavaScript closures is true?

Which statement about JavaScript closures is true?

• A. A closure is a function that has no access to variables from its outer scope.
• B. A closure is a function that retains access to its outer scope, even after the outer function has returned.
• C. A closure is the same as a global variable.
• D. A closure can only be created at compile time.

Answer: (B)

The idea being tested is that a function can remember and continue to access variables from the scope where it was created, even after that outer scope has finished. This is what a closure does: when you define a function inside another function, the inner function closes over the outer function’s variables. Those bindings stay alive as part of the inner function’s internal environment, so the inner function can read or modify them later, long after the outer function has returned. For example, a function factory creates a new function that keeps its own private state. If you set up a counter this way, each time the inner function runs, it updates the saved count and returns it, even though the outer function has already completed. This happens because the inner function retains access to the outer scope’s variables through the closure. Closures are not the same as global variables, and they aren’t created only at compile time. They arise at runtime whenever a function is defined inside another function and captures variables from that outer scope, allowing those variables to persist beyond the outer function’s execution. This concept is useful for creating private state, factory functions, and patterns like modules or iterators, where you want a function to have access to some data that isn’t exposed globally.

The idea being tested is that a function can remember and continue to access variables from the scope where it was created, even after that outer scope has finished. This is what a closure does: when you define a function inside another function, the inner function closes over the outer function’s variables. Those bindings stay alive as part of the inner function’s internal environment, so the inner function can read or modify them later, long after the outer function has returned.

For example, a function factory creates a new function that keeps its own private state. If you set up a counter this way, each time the inner function runs, it updates the saved count and returns it, even though the outer function has already completed. This happens because the inner function retains access to the outer scope’s variables through the closure.

Closures are not the same as global variables, and they aren’t created only at compile time. They arise at runtime whenever a function is defined inside another function and captures variables from that outer scope, allowing those variables to persist beyond the outer function’s execution.

This concept is useful for creating private state, factory functions, and patterns like modules or iterators, where you want a function to have access to some data that isn’t exposed globally.