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Example

const cars = ["Saab", "Volvo", "BMW"]; Try it Yourself »

An Array is an object type designed for storing data collections.

Key characteristics of JavaScript arrays are:

Elements: An array is a list of values, known as elements.
Ordered: Array elements are ordered based on their index.
Zero indexed: The first element is at index 0, the second at index 1, and so on.
Dynamic size: Arrays can grow or shrink as elements are added or removed.
Heterogeneous: Arrays can store elements of different data types (numbers, strings, objects and other arrays).

Why Use Arrays?

If you have a list of items (a list of car names, for example), storing the names in single variables could look like this:

let car1 = "Saab"; let car2 = "Volvo"; let car3 = "BMW";

However, what if you want to loop through the cars and find a specific one? And what if you had not 3 cars, but 300?

The solution is an array!

An array can hold many values under a single name, and you can access the values by referring to an index number.

Creating an Array

Using an array literal is the easiest way to create a JavaScript Array.

Syntax:

const array_name = [item1, item2, ...];

Note

It is a common practice to declare arrays with the const keyword.

Learn more about const with arrays in the chapter: JS Array Const.

Example

const cars = ["Saab", "Volvo", "BMW"]; Try it Yourself »

Spaces and line breaks are not important. A declaration can span multiple lines:

Example

const cars = [ "Saab", "Volvo", "BMW" ]; Try it Yourself »

You can also create an empty array, and provide elements later:

Example

const cars = []; cars[0]= "Saab"; cars[1]= "Volvo"; cars[2]= "BMW"; Try it Yourself »

Using the JavaScript Keyword new

The following example also creates an Array, and assigns values to it:

Example

const cars = new Array("Saab", "Volvo", "BMW"); Try it Yourself »

Note

The two examples above do exactly the same.

There is no need to use new Array().

For simplicity, readability and execution speed, use the array literal method.

Accessing Array Elements

You access an array element by referring to the index number:

const cars = ["Saab", "Volvo", "BMW"]; let car = cars[0]; Try it Yourself »

Note: Array indexes start with 0.

[0] is the first element. [1] is the second element.

Changing an Array Element

This statement changes the value of the first element in cars:

cars[0] = "Opel";

Example

const cars = ["Saab", "Volvo", "BMW"]; cars[0] = "Opel"; Try it Yourself »

Converting an Array to a String

The JavaScript method toString() converts an array to a string of (comma separated) array values.

Example

const fruits = ["Banana", "Orange", "Apple", "Mango"]; document.getElementById("demo").innerHTML = fruits.toString();

Result:

Banana,Orange,Apple,Mango Try it Yourself »

Access the Full Array

With JavaScript, the full array can be accessed by referring to the array name:

Example

const cars = ["Saab", "Volvo", "BMW"]; document.getElementById("demo").innerHTML = cars; Try it Yourself »

Arrays are Objects

Arrays are a special type of objects. The typeof operator in JavaScript returns "object" for arrays.

But, JavaScript arrays are best described as arrays.

Arrays use numbers to access its "elements". In this example, person[0] returns John:

Array:

const person = ["John", "Doe", 46]; Try it Yourself »

Objects use names to access its "members". In this example, person.firstName returns John:

Object:

const person = {firstName:"John", lastName:"Doe", age:46}; Try it Yourself »

Array Elements Can Be Objects

JavaScript variables can be objects. Arrays are special kinds of objects.

Because of this, you can have variables of different types in the same Array.

You can have objects in an Array. You can have functions in an Array. You can have arrays in an Array:

myArray[0] = Date.now; myArray[1] = myFunction; myArray[2] = myCars;

Array Properties and Methods

The real strength of JavaScript arrays are the built-in array properties and methods:

cars.length // Returns the number of elements cars.sort() // Sorts the array

Array methods are covered in the next chapters.

The length Property

The length property of an array returns the length of an array (the number of array elements).

Example

const fruits = ["Banana", "Orange", "Apple", "Mango"]; let length = fruits.length; Try it Yourself »

The length property is always one more than the highest array index.

Accessing the First Array Element

Example

const fruits = ["Banana", "Orange", "Apple", "Mango"]; let fruit = fruits[0]; Try it Yourself »

Accessing the Last Array Element

Example

const fruits = ["Banana", "Orange", "Apple", "Mango"]; let fruit = fruits[fruits.length - 1]; Try it Yourself »

Looping Array Elements

One way to loop through an array, is using a for loop:

Example

const fruits = ["Banana", "Orange", "Apple", "Mango"]; let fLen = fruits.length; let text = "<ul>";for (let i = 0; i < fLen; i++) { text += "<li>" + fruits[i] + "</li>";}text += "</ul>"; Try it Yourself »

You can also use the Array.forEach() function:

Example

const fruits = ["Banana", "Orange", "Apple", "Mango"]; let text = "<ul>";fruits.forEach(myFunction);text += "</ul>"; function myFunction(value) { text += "<li>" + value + "</li>";} Try it Yourself »

Adding Array Elements

The easiest way to add a new element to an array is using the push() method:

Example

const fruits = ["Banana", "Orange", "Apple"]; fruits.push("Lemon"); // Adds a new element (Lemon) to fruits Try it Yourself »

New element can also be added to an array using the length property:

Example

const fruits = ["Banana", "Orange", "Apple"]; fruits[fruits.length] = "Lemon"; // Adds "Lemon" to fruits Try it Yourself »

WARNING !

Adding elements with high indexes can create undefined "holes" in an array:

Example

const fruits = ["Banana", "Orange", "Apple"]; fruits[6] = "Lemon"; // Creates undefined "holes" in fruits Try it Yourself »

Associative Arrays

Many programming languages support arrays with named indexes.

Arrays with named indexes are called associative arrays (or hashes).

JavaScript does not support arrays with named indexes.

In JavaScript, arrays always use numbered indexes.

Example

const person = []; person[0] = "John"; person[1] = "Doe"; person[2] = 46; person.length; // Will return 3 person[0]; // Will return "John" Try it Yourself »

WARNING !! If you use named indexes, JavaScript will redefine the array to an object.

After that, some array methods and properties will produce incorrect results.

Example:

const person = []; person["firstName"] = "John"; person["lastName"] = "Doe"; person["age"] = 46; person.length; // Will return 0 person[0]; // Will return undefined Try it Yourself »

The Difference Between Arrays and Objects

In JavaScript, arrays use numbered indexes.

In JavaScript, objects use named indexes.

Arrays are a special kind of objects, with numbered indexes.

When to Use Arrays. When to use Objects.

JavaScript does not support associative arrays.
You should use objects when you want the element names to be strings (text).
You should use arrays when you want the element names to be numbers.

JavaScript new Array()

JavaScript has a built-in array constructor new Array().

But you can safely use [] instead.

These two different statements both create a new empty array named points:

const points = new Array(); const points = [];

These two different statements both create a new array containing 6 numbers:

const points = new Array(40, 100, 1, 5, 25, 10); const points = [40, 100, 1, 5, 25, 10]; Try it Yourself »

The new keyword can produce some unexpected results:

// Create an array with three elements: const points = new Array(40, 100, 1); Try it Yourself » // Create an array with two elements: const points = new Array(40, 100); Try it Yourself » // Create an array with one element ??? const points = new Array(40); Try it Yourself »

A Common Error

const points = [40];

is not the same as:

const points = new Array(40); // Create an array with one element: const points = [40]; Try it Yourself » // Create an array with 40 undefined elements: const points = new Array(40); Try it Yourself »

How to Recognize an Array

A common question is: How do I know if a variable is an array?

The problem is that the JavaScript operator typeof returns "object":

const fruits = ["Banana", "Orange", "Apple"]; let type = typeof fruits; Try it Yourself »

The typeof operator returns object because a JavaScript array is an object.

Solution 1:

To solve this problem ECMAScript 5 (JavaScript 2009) defined a new method Array.isArray():

Array.isArray(fruits); Try it Yourself »

Solution 2:

The instanceof operator returns true if an object is created by a given constructor:

const fruits = ["Banana", "Orange", "Apple"]; (fruits instanceof Array); Try it Yourself »

Nested Arrays and Objects

Values in objects can be arrays, and values in arrays can be objects:

Example

const myObj = { name: "John", age: 30, cars: [ {name:"Ford", models:["Fiesta", "Focus", "Mustang"]}, {name:"BMW", models:["320", "X3", "X5"]}, {name:"Fiat", models:["500", "Panda"]} ]}

To access arrays inside arrays, use a for-in loop for each array:

Example

for (let i in myObj.cars) { x += "<h1>" + myObj.cars[i].name + "</h1>"; for (let j in myObj.cars[i].models) { x += myObj.cars[i].models[j]; }} Try it Yourself »

Learn More:

Basic Array Methods

Array Search Methods

Array Sort Methods

Array Iteration Methods

JavaScript Array Reference

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