What is an IIFE and when would you use one?

Quick answer

An Immediately Invoked Function Expression runs the moment it's defined, creating a private scope.

In detail

Before ES modules, IIFEs were the main way to avoid polluting the global namespace and to create private state. Wrapping code in `(function(){ ... })()` gives it its own scope. Today modules cover most of this, but IIFEs still appear in bundlers and one-off initialisation.

const api = (function () {
  let secret = 0;            // private
  return { bump: () => ++secret };
})();
api.bump(); // 1 — secret is inaccessible outside

Why interviewers ask this: Tests understanding of scope isolation and history.

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