JS ARRAY OBJECT

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

Displaying Arrays

In this tutorial we will use a script to display arrays inside a <p> element with id="demo":

<p id="demo"></p>

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

The first line (in the script) creates an array named cars.

The second line "finds" the element with id="demo", and "displays" the array in the "innerHTML" of it.

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, ...];

Example:

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 refer to an array element by referring to the index number.

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

var name = cars[0];

This statement modifies the first element in cars:

cars[0] = "Opel";

[0] is the first element in an array. [1] is the second. Array indexes start with 0.

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;

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:

var person = ["John", "Doe", 46];

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 elements in cars
var y = cars.sort(); // The sort() method sort cars in alphabetical order

Array methods are covered in the next chapter.

The length Property

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

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.length; // the length of fruits is 4

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

Adding Array Elements

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

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

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

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

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

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits[10] = "Lemon"; // adds a new element (Lemon) to fruits

Looping Array Elements

The best 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>";
}