JavaScript Arrays

JavaScript arrays are used to store multiple values in a single variable.

var cars = ["Saab", "Volvo", "BMW"];

What is an Array?

An array is a special variable, which can hold more than one value at a time.

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

var car1 = "Saab";
var car2 = "Volvo";
var 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:

var array_name = [item1, item2, ...];

var cars = ["Saab", "Volvo", "BMW"];

Using the JavaScript Keyword new

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

var cars = new Array("Saab", "Volvo", "BMW");

Access the Elements of an Array

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

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

var name = cars[0];

var cars = ["Saab", "Volvo", "BMW"];
document.getElementById("demo").innerHTML = cars[0];

Changing an Array Element

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

cars[0] = "Opel";

var cars = ["Saab", "Volvo", "BMW"];
cars[0] = "Opel";
document.getElementById("demo").innerHTML = cars[0];

Access the Full Array

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

var cars = ["Saab", "Volvo", "BMW"];
document.getElementById("demo").innerHTML = cars;

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:

var person = ["John", "Doe", 46];

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:

var x = cars.length;   // The length property returns the number of elementsvar y = cars.sort();   // The sort() method sorts arrays

Looping Array Elements

The safest way to loop through an array, is using a "for" loop:

var fruits, text, fLen, i;
fruits = ["Banana", "Orange", "Apple", "Mango"];
fLen = fruits.length;

text = "<ul>";
for (i = 0; i < fLen; i++) {
    text += "<li>" + fruits[i] + "</li>";
}
text += "</ul>";

WARNING !

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

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits[6] = "Lemon";                 // adds a new element (Lemon) to fruits

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.

var person = [];
person[0] = "John";
person[1] = "Doe";
person[2] = 46;
var x = person.length;         // person.length will return 3var y = person[0];             // person[0] will return "John"