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What you mean by closers in javascript? - javascript in

What you mean by closers in javascript? - javascript in And How does the same works?
What you mean by closers in javascript? - javascript in And How does the same works?

Asked On2021-10-09 13:08:52 by:sharma

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A closure is the 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.

Consider the following example
function makeAdder(x) {
  return function(y) {
    return x + y;

var add5 = makeAdder(5);
var add10 = makeAdder(10);

console.log(add5(2));  // 7 
console.log(add10(2)); // 12
add5 and add10 are both closures. They share the same function body definition, but store different lexical environments. In add5's lexical environment, x is 5, while in the lexical environment for add10x is 10.
 Lets Dig deep into these concepts. Execution ContextLexical Environment, and Identifier Resolution This will give us better understanding of what we are actually dealing with.
Execution Context
every time we call a function, a new execution context is created and is put on top of the execution stack. The same pattern follows when you call the nested function which calls another nested function:

Lexical Environment
A Lexical Environment is a specification type used to define the association of Identifiers to specific variables and functions based upon the lexical nesting structure of ECMAScript code
Identifier Resolution
Lets check the below snippet of code and try to understand what is an identifier resolution from the same.
var x = 10;
function foo(){
var y = 20;
console.log(x+y); // 30
// Environment technically consist of two main components:
// environmentRecord, and a reference to the outer environment
// Environment of the global context
globalEnvironment = {
environmentRecord: {
// built-ins
// our bindings:
x: 10
outer: null // no parent environment
// Environment of the "foo" function
fooEnvironment = {
environmentRecord: {
y: 20
outer: globalEnvironment

As you can see when trying to resolve the identifier “x” in the foo context, the outer environment (global) is reached out. This process is called identifier resolution and happens on running execution context.
This will give us better understanding of what we are actually dealing with.

Answerd on:2021-10-10 Answerd By:batsam22

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