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   • Closure in JavaScript

     JavaScript closure is a feature that allows inner functions to access the outer scope of a function. Closure helps in binding a function to its outer boundary and is created automatically whenever a function is created. A block is also treated as a scope since ES6. Since JavaScript is event-driven so closures are useful as it helps to maintain the state between events.

     Prerequisite:

     Variable Scope in JavaScript 

     A function scope’s ability to access variables from the parent scope is known as lexical scope. We refer to the parent function’s lexical binding of the child function as “lexically binding.”

     Let’s see and understand closure through an example. 

     Example 1: This example shows the basic use of closure.

     Javascript

     function foo() {    let b = 1;    function inner() {        return b;    }    return inner;}let get_func_inner = foo(); console.log(get_func_inner());console.log(get_func_inner());console.log(get_func_inner());-

     Output:

     We can access the variable b which is defined in the function foo() through function inner() as the later preserves the scope chain of the enclosing function at the time of execution of the enclosing function i.e. the inner function...

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   • Closure with parameter in Javascript

     Top Answer

     Answered Oct 17, 2016 · 4 votes

     When you use brackets () after a function, it gets executed immediately. And in this case you have not passed any parameter there.

     It can go two ways.

     var closureFunction = function(var1,var2){ var privateVar = var1+var2; - console.log("Sum of "+ var1 +" and "+ var2+""); return function(){return privateVar;} }(2,3); //prints 'Sum of 2 and 3' console.log(closureFunction()); //prints '5'

     Or you can pass parameters in steps

     var closureFunction = function(var1){ - return function(var2 ){ console.log("Sum of "+ var1 +" and "+ var2+""); return var1 + var2; } }(2); //just return a 'closure' functionconsole.log(closureFunction(3)); //prints 'Sum of 2 and 3 5'

     or you can execute it later.

     var closureFunction = function(var1){ - return function(var2 ){ console.log("Sum of "+ var1 +" and "+ var2+""); return var1 + var2; } }; var x = closureFunction(2); //return a 'closure' functionconsole.log(x(3)); //prints 'Sum of 2 and 3 5'

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   • Closure memory leak patterns in JavaScript

     Top Answer

     Answered Jun 10, 2014 · 3 votes

     As given, none of those will create memory leaks.

     Leaks are held by not releasing memory -- everything there gets released.

     By the way, none of the code you are showing uses closures.

     Now, here are a handful of ways that "leaks" can be created.

     // Simple leak -- an array that never lets go of memoryvar arrayThatNeverShrinks = [];function doleak() { var s = "1234567890"; arrayThatNeverShrinks.push(s); window.setTimeout(doleak, 500);}//start if offdoleak();// This function leaks because bigVar is used -- and kept -- // inside of the anonymous function inside. //Another leak, using closures var leakingFunction = (function() { var bigVar = "1234567890"; return function() { alert("Hi there"); var keepBigVar = bigVar; } }());

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   • JavaScript Closure in Loop

     Top Answer

     Answered May 10, 2015 · 9 votes

     Your i and x values are declared in exactly the same scope, so by the time the function is executed x will be its final value. You could create a closure like this:

     function registerHandlers() { var links = document.getElementsByTagName('a');- for (var i = 0, len = links.length; i < len; i += 1) { links[i].onclick = generateHandler(i); } function generateHandler (index) { return function () { alert(index); return false; } }}

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2. developer.mozilla.org › Web › JavaScriptClosures - JavaScript | MDN - MDN Web Docs

   developer.mozilla.org › Web › JavaScript

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   Nov 8, 2023 · 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.

3. www.w3schools.com › js › js_function_closuresJavaScript Function Closures - W3Schools

   www.w3schools.com › js › js_function_closures

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   Learn how to use closures to create private variables in JavaScript. A closure is a function that can access the parent scope, even after the parent function has closed. See examples, explanations and exercises.

4. www.freecodecamp.org › news › closures-in-javascriptClosures in JavaScript Explained with Examples - freeCodeCamp.org

   www.freecodecamp.org › news › closures-in-javascript

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   Feb 18, 2020 · Learn what closures are and how they work in JavaScript with code examples. Closures are the combination of a function and the lexical environment within which it was declared, and they can be used for private methods, data encapsulation, and block-scoped variables.

5. www.geeksforgeeks.org › closure-in-javascriptClosure in JavaScript - GeeksforGeeks

   www.geeksforgeeks.org › closure-in-javascript

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   May 6, 2024 · Learn what closure is, how it works, and why it is useful in JavaScript. See examples of creating closures, accessing outer function variables, and using closures for state, private variables, and callbacks.

6. javascript.info › closureVariable scope, closure - The Modern JavaScript Tutorial

   javascript.info › closure

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   Jun 13, 2022 · Learn how functions can access and modify variables outside of them in JavaScript. Understand the concepts of variable scope, code blocks, and closure with examples and exercises.

7. People also ask

   When are closures created in JavaScript?

   • In JavaScript, closures are created every time a function is created, at function creation time. Consider the following example code: console.log(name); // use variable declared in the parent function } displayName(); } init(); init() creates a local variable called name and a function called displayName().

   Closures - JavaScript | MDN - MDN Web Docs

   developer.mozilla.org/en-US/docs/Web/JavaScript/Closures

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   Why do JavaScript functions form closures?

   • The reason is that functions in JavaScript form closures. A closure is the combination of a function and the lexical environment within which that function was declared. This environment consists of any local variables that were in-scope at the time the closure was created.

   Closures - JavaScript | MDN - MDN Web Docs

   developer.mozilla.org/en-US/docs/Web/JavaScript/Closures

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   What is a closure in programming?

   • There is a general programming term “closure”, that developers generally should know. A closure is a function that remembers its outer variables and can access them. In some languages, that’s not possible, or a function should be written in a special way to make it happen.

   Variable scope, closure - The Modern JavaScript Tutorial

   javascript.info/closure

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   What is a closure in Java?

   • A closure is a function having access to the parent scope, even after the parent function has closed. Well organized and easy to understand Web building tutorials with lots of examples of how to use HTML, CSS, JavaScript, SQL, Python, PHP, Bootstrap, Java, XML and more.

   JavaScript Function Closures - W3Schools

   www.w3schools.com/js/js_function_closures.asp

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8. www.javascripttutorial.net › javascript-closureThe Beginner's Guide to JavaScript Closure and Its Usages

   www.javascripttutorial.net › javascript-closure

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   Learn what closures are and how to use them in JavaScript. A closure is a function that references variables in the outer scope from its inner scope. See examples of closures, lexical scoping, and how to avoid common pitfalls.

9. www.freecodecamp.org › news › closures-in-javascriptHow to Use Closures in JavaScript – A Beginner's Guide

   www.freecodecamp.org › news › closures-in-javascript

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   Jun 7, 2021 · Learn what closures are and how to use them in JavaScript with examples and explanations. Closures are functions that access variables defined outside their context, and can be used for modules, function factories, currying, and more.