How do JavaScript closures work?

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Sleepy Squirrel answered on January 18, 2020 Popularity 10/10 Helpfulness 2/10

answer How do JavaScript closures work?

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How do JavaScript closures work?

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/*
A lexical environment is part of every execution context (stack frame) and is a map between identifiers (i.e. local variable names) and values.

Every function in JavaScript maintains a reference to its outer lexical environment. This reference is used to configure the execution context created when a function is invoked. 
This reference enables code inside the function to "see" variables declared outside the function, regardless of when and where the function is called.

If a function was called by a function, which in turn was called by another function, then a chain of references to outer lexical environments is created.
This chain is called the scope chain.

In the following code, inner forms a closure with the lexical environment of the execution context created when foo is invoked, closing over variable secret:
*/
function foo() {
  const secret = Math.trunc(Math.random() * 100)
  return function inner() {
    console.log(`The secret number is ${secret}.`)
  }
}
const f = foo() // `secret` is not directly accessible from outside `foo`
f() // The only way to retrieve `secret`, is to invoke `f`
 Run code snippet

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Source: stackoverflow.com

Tags: closures javascript

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Contributed on Jun 22 2022

Sleepy Squirrel

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closures in javascript

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// A closure is a function having access to the parent scope, 
// even after the parent function has popped.

function greeting() {
    let message = 'Hi';

    function sayHi() {
        console.log(message);
    }

    return sayHi;
}
let hi = greeting();
hi(); // still can access the message variable

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Source: www.javascripttutorial.net

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Contributed on Feb 01 2022

madhav

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closure in javascript

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-->closure in javascript
//closure is the combination of function and the lexical enviornment in
//which the function is defined.closure give you access to the functions
//and variables outside the function.
function outer(){
  const outerData ="outer";
  function inner(){
    const innerData="inner";
    console.log(`${outerData} and{innerData}`);
  }
  inner();
}
outer();

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Tags: javascript j

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Contributed on Dec 22 2021

tokyo

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javascript closure

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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

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Contributed on Jan 18 2020

Grieving Goshawk

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closure in javascript

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function makeFunc() {
  var name = 'Mozilla';
  function displayName() {
    alert(name);
  }
  return displayName;
}

var myFunc = makeFunc();
myFunc();

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Source: developer.mozilla.org

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Contributed on Jul 04 2020

Black Buzzard

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closure example in javascript

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function outerFunction() {
  var outerVariable = 'I am an outer variable';

  function innerFunction() {
    var innerVariable = 'I am an inner variable';
    console.log(outerVariable);
  }

  return innerFunction;
}

var closureExample = outerFunction();
closureExample();

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Contributed on Sep 11 2023

YOU.com

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Closures in javascript

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let counter = (function() {
    let i = 0; // private property

    return {   // public methods
        get: function() {
            alert(i);
        },
        set: function(value) {
            i = value;
        },
        increment: function() {
            alert(++i);
        }
    };
})(); // module

counter.get();      // shows 0
counter.set(6);
counter.increment(); // shows 7
counter.increment(); // shows 8

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Source: en.wikipedia.org

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Contributed on Apr 29 2022

Ali Salman

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Javascript Closure

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function makeFunc() {
  var name = 'Mozilla';
  function displayName() {
    alert(name);
  }
  return displayName;
}

var myFunc = makeFunc();
myFunc();

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Source: developer.mozilla.org

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Contributed on Jun 17 2022

Peter Ime

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javascript closure

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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

//my words: what this code do is basically a nested function that will return
//its inner function (un-activated). So var add5 in line 7 activated the outer
//function with 5 as parameter which makes add5 is now the nameless function at
//line 2 that will return 5 + y;

//MDN words:
//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 add10, x is 10.

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Contributed on Jan 20 2022

Graceful Grivet

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what is closure in JavaScript

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A combination of a function object and a scope (a set of variable bindings)

in which the function's variables are resolved is called a closure.

Callbacks are functions that are passed into another function as an argument.

Closures are functions that are nested in other functions, and it's often used to avoid scope clash

with other parts of a JavaScript program

<button type="button" onclick="funClosure()">Click to Count</button>

<p id="displayValue">0</p>
<script>
const add = (function(){
	let count = 0;
    return function(){
		count += 1;
        return count;
    }
})();

function funClosure(){
  document.getElementById("displayValue").innerHTML = add();
}
</script>

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Contributed on Mar 31 2023

@CodeGrepperManu

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JavaScript Closures

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// javascript closure example

// outer function
function greet() {
    // variable defined outside the inner function
    let name = 'John';
    // inner function
    function displayName() {

        // accessing name variable
        return 'Hi' + ' ' + name;
      
    }
    return displayName;
}

const g1 = greet();
console.log(g1); // returns the function definition
console.log(g1()); // returns the value

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Contributed on May 22 2022

SAMER SAEID

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How do JavaScript closures work?

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