How to Iterate through an Array in JavaScript

How to Iterate through an Array in JavaScript

How to Iterate through an Array in JavaScript

In this post, we will give you information about How to Iterate through an Array in JavaScript. Here we will give you detail about How to Iterate through an Array in JavaScript And how to use it also give you a demo for it if it is necessary.

There are several ways to iterate through an array in JavaScript, and there’s a lot
of debate about which way is the right way. Generally speaking, there are 4 common

  1. Simple for Loop: for (let i = 0; i < arr.length; ++i)
  2. Functional methods like forEach(): arr.forEach((v, i) => { /* ... */ })
  3. The for-of loop: for (const v of arr)
  4. The for-in loop: for (const i in arr)

Below are several of the most important differences between the 4 common approaches.

TLDR: Prefer to use for-of (3) where possible. Simple for loop (1) is OK as well. Do not use for/in.

Async/Await Support

The big gotcha with functional methods like forEach() is that, because you pass a
separate function to forEach(), using async/await with forEach() is hard. For example,
the below code will print the numbers 0-9 in reverse order, because forEach() executes
async functions in parallel and doesn’t give you a way to handle errors.

async function print(n) {
  // Wait 1 second before printing 0, 0.9 seconds before printing 1, etc.
  await new Promise(resolve => setTimeout(() => resolve(), 1000 - n * 100));
  // Will usually print 9, 8, 7, 6, 5, 4, 3, 2, 1, 0 but order is not strictly
  // guaranteed.

async function test() {
  [0, 1, 2, 3, 4, 5, 6, 7, 8, 9].forEach(print);


On the other hand, async functions work great with JavaScript’s built-in loops.

async function print(n) {
  await new Promise(resolve => setTimeout(() => resolve(), 1000 - n * 100));

async function test() {
  // Prints 0-9 in order.
  for (const num of [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]) {
    await print(num);


Non-Numeric Properties

JavaScript arrays are objects. typeof [] === 'object'. That means arrays can have
non-numeric properties. The primary reason to avoid using for/in is that for/in
iterates over non-numeric properties, whereas for, forEach(), and for/of skip non-numeric properties.

const arr = ['a', 'b', 'c'];
arr['bad'] = 'alpha';

for (let key in arr) {
  console.log(arr[key]); // Prints: a, b, c, alpha

// However, 'for/of' skips non-numeric keys
for (const val of arr) {
  console.log(val); // Prints: a, b, c

// So does 'forEach()'
arr.forEach(val => console.log(val)); // Prints: a, b, c

const Iterator Key for How to Iterate through an Array in JavaScript

One common mistake when using simple for loops is unintentionally incrementing i.
I’ve lost count of the number of times I’ve accidentally incremented the wrong counter
in a nested for loop.

for (let i = 0; i < arr.length; ++i) {
  // So easy to accidentally type '++i' below.
  for (let j = 0; j < arr.length; ++i) {


forEach(), for/of, and for/in have the nice advantage of being able to prevent
messing up the loop by accidentally modifying the loop index. With forEach(), you can
modify the index argument, but that has no affect on the loop. With for/of and for/each,
you can mark the iterator key as a const.

for (const [i, el] of Object.entries(arr)) {
  ++i; // Compile time error

Summary for How to Iterate through an Array in JavaScript

Below is a chart comparing the looping constructs:

You should prefer to use for/of unless you have a good reason not to. You may
want to use forEach() for some neat syntactic sugar with filter() and map(), or you
may actually want to loop through non-numeric properties on an array and use for/in. But
for/of is the most robust approach and works well for almost all cases.


JavaScript Fundamentals for How to Iterate through an Array in JavaScript

JavaScript is a programming language that is used to create interactive web pages. It is a client-side scripting language, which means that it runs on the user’s browser. JavaScript can be used to add animation, interactivity, and functionality to web pages.

Here are some of the fundamentals of JavaScript:

  • Variables: Variables are used to store data. They are declared using the var keyword.
  • Data types: JavaScript has a variety of data types, including strings, numbers, booleans, objects, and arrays.
  • Operators: Operators are used to perform operations on data.
  • Control flow statements: Control flow statements allow you to control the order in which your code is executed.
  • Functions: Functions are blocks of code that can be reused.
  • Objects: Objects are used to store data in key-value pairs.
  • Arrays: Arrays are used to store data in a sequential order.
  • Events and event handlers: Events are notifications that are sent by the browser when something happens, such as when the user clicks on an element or moves the mouse over an element. Event handlers are functions that are called in response to an event.
  • DOM manipulation: The Document Object Model (DOM) is a tree-like structure that represents the elements of a web page. JavaScript can be used to manipulate the DOM to change the appearance or behavior of a web page.

These are just some of the fundamentals of JavaScript. There are many other concepts that you can learn as you continue to develop your skills.

Here are some resources that you can use to learn more about JavaScript:

  • Mozilla Developer Network (MDN): The MDN is a great resource for learning about JavaScript. It has a comprehensive reference guide, tutorials, and articles on a wide range of topics.
  • W3Schools: W3Schools is another great resource for learning about JavaScript. It has interactive tutorials and quizzes that can help you learn the basics of the language.
  • is a website that provides in-depth tutorials on JavaScript. It also has a forum where you can ask questions and get help from other JavaScript developers.

I hope this helps!

Here are some additional tips for learning JavaScript:

  • Start with the basics: Before you start trying to build complex applications, it’s important to learn the basics of JavaScript. This includes things like variables, data types, operators, and control flow statements.
  • Practice regularly: The best way to learn JavaScript is to practice regularly. Try to find some time each day to work on JavaScript projects.
  • Get help from others: If you get stuck, don’t be afraid to ask for help from others. There are many online forums and communities where you can get help from other JavaScript developers.

With a little practice, you’ll be able to learn JavaScript and start building amazing web applications.

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