Closures in JavaScript

Direct Answer

A closure is a function bundled with references to variables from its lexical outer scope. It can continue to read or update those variables after the outer function has returned, which enables factories, private state, and callbacks.

Deep Dive & Architecture

A closure is a function bundled with references to variables from its lexical outer scope.

It can continue to read or update those variables after the outer function has returned, which enables factories, private state, and callbacks.

A closure keeps access to the lexical environment where it was created. The outer function may finish, but the captured binding remains reachable through the inner function.

Saying a closure copies values rather than retaining access to the environment.

Code Example

function makeCounter() {
  let count = 0;
  return () => ++count;
}
const next = makeCounter();
next(); // 1
next(); // 2

Common Mistakes & Pitfalls

Saying a closure copies values rather than retaining access to the environment.