Closures

Closures

A closure is a function that remembers the variables from the scope where it was created, even after that scope is gone.

The classic example

function makeCounter() {
  let count = 0;
  return function() {
    count++;
    return count;
  };
}

const counter = makeCounter();
counter(); // 1
counter(); // 2
counter(); // 3

What is happening?

• makeCounter creates a local variable count.
• It returns an inner function.
• The inner function "closes over" count and keeps it alive.
• Each call to counter() can still access and update count.

Why closures matter

• Create private variables that other code cannot touch.
• Build functions that remember state.
• Used everywhere: counters, event handlers, and module patterns.

Private variables

The variable count is not accessible from outside, only through the closure:

counter.count; // undefined

TL;DR

• A closure is a function plus its remembered scope.
• Inner functions keep access to outer variables.
• Closures create private state.
• Great for counters and encapsulating data.