Why does for (var i = 0; i < 3; i++) setTimeout(() => console.log(i), 0) log 3, 3, 3?
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.
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More FAQs in 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.
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.
Create a cache object in the outer function. Return a function that checks the cache for the arguments (serialized as a key). If not found, call the original function and store the result. Return the cached result.
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