The for statement creates a loop that consists of three optional expressions, enclosed in parentheses and separated by semicolons, followed by a statement (usually a block statement) to be executed in the loop.

This feature is well established ... since July 2015. ... The for...in statement iterates over all enumerable string properties of an object (ignoring properties keyed by symbols), including inherited enumerable properties....

The for...of statement executes a loop that operates on a sequence of values sourced from an iterable object. Iterable objects include instances of built-ins such as Array, String, TypedArray, Map, Set, NodeList (and other DOM collections), as well as the arguments object, generators produced ...

JavaScript (JS) is a lightweight interpreted (or just-in-time compiled) programming language with first-class functions. While it is most well-known as the scripting language for Web pages, many non-browser environments also use it, such as Node.js, Apache CouchDB and Adobe Acrobat.

The for...in loop is primarily used for objects to access their property names (keys). for (key in object) { // code block to be executed } key A variable that holds the name (key) of each property during the iterations · object The object ...

Do not use for...in to iterate an array if the index order is important. Use a for loop instead. ... If you want to use W3Schools services as an educational institution, team or enterprise, send us an e-mail: sales@w3schools.com · If you want to report an error, or if you want to make a suggestion, send us an e-mail: help@w3schools.com · HTML Tutorial CSS Tutorial JavaScript Tutorial How To Tutorial SQL Tutorial Python Tutorial W3.CSS Tutorial Bootstrap Tutorial PHP Tutorial Java Tutorial C++ Tutorial jQuery Tutorial

The JavaScript for...in loop iterates over the keys of an object. In this tutorial, you will learn about the JavaScript for...in loop with the help of examples.

When let is used to declare the i variable in a loop, the i variable will only be visible within the loop. ... If you want to use W3Schools services as an educational institution, team or enterprise, send us an e-mail: sales@w3schools.com · If you want to report an error, or if you want to make a suggestion, send us an e-mail: help@w3schools.com · HTML Tutorial CSS Tutorial JavaScript Tutorial How To Tutorial SQL Tutorial Python Tutorial W3.CSS Tutorial Bootstrap Tutorial PHP Tutorial Java Tutorial C++ Tutorial jQuery Tutorial

January 12, 2026 - JavaScript is a scripting or programming language that allows you to implement complex features on web pages — every time a web page does more than just sit there and display static information for you to look at — displaying timely content updates, interactive maps, animated 2D/3D graphics, ...

The two most distinct are the classic for loop and the for...in loop. ... Become a full-stack developer. Learn HTML, CSS, JavaScript, and React as well as NodeJS, Express, and SQL ... Master the language of the web. Learn variables, functions, objects, and modern ES6+ features ... Classic for loop: Repeats a block of code a specific number of times. It is commonly used to iterate over an array using its index.

August 6, 2024 - Most web browsers run JavaScript to create dynamically updating content, control multimedia, and animate images. Coders use it to build games, calculators, and other programs for websites.

December 6, 2024 - Understanding the distinction between for...in and for...of statements is vital for writing clear and efficient JavaScript code. While for...in excels at iterating over object properties, for...of is the go-to choice for iterable objects like arrays.

May 13, 2025 - JavaScript is a programming language that enables dynamic interactions on websites. It’s a cornerstone technology of the web, alongside HTML and CSS, and is essential for creating interactive web applications.

The JavaScript for of statement loops through the values of an iterable object. It lets you loop over iterable data structures such as Arrays, Strings, Maps, NodeLists, and more: for (variable of iterable) { // code block to be executed } variable ...

February 4, 2025 - Where the HTML and CSS programming languages are used to give websites their structure and style, JavaScript is used to take static web applications and brings them to life, greatly improving the user experience in the process. Given how popular and ubiquitous JavaScript has become, it sometimes seems like the answer to the question “What is JavaScript used for?” is “everything.”

JavaScript (JS) is a high-level, versatile programming language that adds interactivity and dynamic behavior to websites. It works alongside HTML, which structures content, and CSS, which styles it, forming the three core web technologies.

April 16, 2022 - After doing some research and playing around with some code in my console I finally understood what the main difference was and I wanted to share what I learned. For…in iterates over all the enumerable properties of an object or array. By ...

July 12, 2025 - Although it can also be used to iterate over the indices of an array. Conversely, the for..of loop is intended to iterate directly over values in iterable collections like arrays, strings, Maps, or Sets. The JavaScript for-in loops through the enumerable properties of an object.

September 23, 2025 - Users primarily use it for developing the interactive front-end of web applications, but you can also use it in back-end development in tandem with Node.js. Brendan Eich created JavaScript in 1995 while working at Netscape Communications Corporation.