Closures in JavaScript

A Closure is a combination of a function bundled together (enclosed) with references to its surrounding state (the lexical environment). In other words, a closure gives you access to an outer function’s scope from an inner function. In JavaScript, closures are created every time a function is created, at function creation time.

The closure has three scope chains:

• It has access to its own scope — variables defined between its curly brackets.
• It has access to the outer function’s variables.
• It has access to global variables.

Some Examples Using Closures:

function makeSizer(size) {
  return function() {
    document.body.style.fontSize = size + 'px';
  };
}

var size12 = makeSizer(12);
var size14 = makeSizer(14);
var size16 = makeSizer(16);

size12, size14, and size16 are now functions that resize the body text to 12, 14, and 16 pixels, respectively.