JavaScript Arrays

In most of the programming solutions we have to come accross the situation where we have to store number of values with same data type. For example we  have a list of 150 student names. So in order to hold the names of 150 students we naeed 150 variables like

name1="Amir"
name2="Khan"
name3="John"
....
....
...
name100="Ahmed"

so it becomes very cumbersome to hold and write the 150 variables in a program. In such scenario arrays comes handy.

Arrays are the special type of variable which can hold a list of values under single variable
name. For example above list of 150 student names can be easily defined using arrays. like

student = ["Amir","Khan","John"........................."Ahmed"];

Defining an Array in JavaScript

An array can be considered as collection of variables of same data type. 

In JavaScript array can be declared as below.

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

or

var array_name = new array_name(item1,item2,item3.......);

For example

var student = ["Amir","Khan","John"..................."Ahmed"];
or
var student = new student("Amir","Khan","John"......"Ahmed");

How to access an array in JavaScript

An item in an array is called an element. An element in an array can be accessed using a numeric value called index.
For example in order to access the first element in above array we will write it as below


student[0];


Be remember that the first index of the array starts with 0 hence the last index of the array must be less than one of the total length of the array. For example
if an array contains 5 elements than the index for the last element is 4.

Arrays are Objects

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

JavaScript Methods

toString() method converts the an array into strings separted by commas.

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

pop() and push() methods are used to remove and add the new elements at the end of an array. For example.

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.pop();              // Removes the last element ("Mango") from fruits


and

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

Similarly shift() and unshit() methods are used to remove and add and element at beginning of the array.

var fruits = ["Banana", "Orange", "Apple", "Mango"];
var x = fruits.shift();    // the value of x is "Banana"

and similarly


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

It is also possible to loop through an array elements using for loop and Array.forEach() . For Example.

 

Below is the code snipt for looping through Array using array.forEach function.
var fruits, text;
fruits = ["Banana", "Orange", "Apple", "Mango"];
text = "<ul>";
fruits.forEach(myFunction);
text += "</ul>";
function myFunction(value) {
  text += "<li>" + value + "</li>";
}