What are Closures in JavaScript?

What are Closures in JavaScript?

Ferenc Almasi β€’ Last updated 2020 November 01 β€’ Read time 2 min read
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Closure often confuse people in JavaScript. In one sentence: It is an inner function that has access to the other function's variables. It’s a combination of a function and the lexical environment in which it was declared.

A great example of closures are callbacks. Note the differences between scopes and closures in the following example:

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// Note the differences between scope and closure

// scope: global
var a = 1;

(function one() {
  // scope: one
  // closure: one, global
  var b = 2;

  (function two() {
    // scope: two
    // closure: two, one, global
    var c = 3;

    (function three() {
      // scope: three
      // closure: three, two, one, global
      var d = 4;
      // This will output 10 as we have access to outer enclosing function variables
      console.log(a + b + c + d);
  • The scope refers to the lexical environment of the function
  • While closure encompasses the lexical scope of other enclosing function as well
What are JavaScript closures?
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