What are the most common closure interview questions in JavaScript?

A function that remembers the variables from its lexical scope, even after the outer function has returned. The function object holds a reference to its outer lexical environment, so it can access those variables later.

Because var is function-scoped. All callbacks share one i. By the time the callbacks run, the loop has finished and i is 3. Using let fixes this because let creates a fresh binding per iteration, and each callback closes over its own i.

Use a closure with a done flag. The first call sets done to true and stores the result. Subsequent calls return the stored result without running the function again.