Arrays in JavaScript

Introduction

An array is declared using square-bracketed notation as in the following.

var names = ["Abhi", "Ayush", "Abhijeet"];

To get an element put its index in square brackets (the first index is 0) as in the following.

var names = ["Abhi", "Ayush", "Abhijeet"];
alert(names[0]);
alert(names[1]);
alert(names[2]);

We can also retrieve its length as in the following.

var names = ["Abhi", "Ayush", "Abhijeet"];
alert(names.length);

Methods pop and push

There is a method pop that removes the last item and returns it. Here we will see how the “abhijeet” is being popped off.

var names = ["Abhi", "Ayush", "Abhijeet"];
alert("I remove " + names.pop());
// Now we have ["Abhi", "Ayush"]
alert("Now length is: " + names.length); // Abhijeet is removed

There is another method push that appends an element to the array. Let’s say we’ve forgotten Bittoo as in the following.

var names = ["Abhi", "Ayush"];
names.push("Bittoo");
// now got ["Abhi", "Ayush", "Bittoo"]
alert("Last element is: " + names[names.length - 1]);

Iterating over an array

To iterate over elements, a loop over all indices is usually used as in the following.

var names = ["Ab", "Yogi", "Abhi", "Ayush", "Bittoo"];
for (var i = 0; i < names.length; i++) {
    alert(names[i]);
}

Multidimensional arrays

Here is an example.

var multi = [[10, 20, 30], [40, 50, 60], [70, 80, 90]];
alert(multi[1][1]); // it is the central element

Join and split

• The join method combines an array into a string using a specific separator as in the following.

  var names = ["Ab", "Abhi", "Ayush", "Bittoo"];
  var s = names.join(', ');
  alert(s);
  

• The split method is the reverse of join.

  var names = "Abhi,Ayush,Bittoo";
  var ar = names.split(',');
  // ar is ["Abhi", "Ayush", "Bittoo"]
  alert(ar[0]);
  

Removing from an array

Here is an example

var ar = ["Hello", "Most", "Welcome"];
delete ar[1];
// now ar = ["Hello", undefined, "Welcome"]
alert(ar[1]); // undefined

A delete operator removes a key-value pair. Because an array is just a hash, the slot becomes undefined. We need to remove an item without leaving holes between indexes. For this, there is another method known as a splice.

Method splice

Syntax

ar.splice(index, deleteCount[, elem1,..., elemN]) 

It can delete elements and replace them.

Here is an example.

var ar = ["Hello", "Most", "Welcome"]  
ar.splice(1, 1) // remove 1st element starting at index 1  
alert(ar.join(',')) // ["Hello", "Welcome"] (1st element removed) 

Another example

Splice is able to insert elements, just set the deleteCount to 0.  
var ar = ["Hello", "Most", "Welcome"];  
// from 2nd position  
// delete 0  
// and insert "Hi", "Buddy"  
ar.splice(2, 0, "Hi", "Buddy")  
alert(ar) // "Hello", "Most", "Hi", "Buddy", "Welcome" 

Method slice

We can also extract a portion of an array using slice(begin, end). This method does not modify the array, it just copies a slice of it.

Example

var ar1 = ["Hello", "Most", "Welcome"];  
var ar2 = ar1.slice(0, 2) // take 2 elements starting at 0  
alert(ar2.join(', ')) // "Hello, Most" 

Method reverse

Suppose I want the last part of a domain, like “com” from “www.abhijeet.com”.

Example

var domname = "www.abhijeet.com"  
var l = domname.split('.').reverse()[0]  
alert(l)