Arrays in JavaScript

Abhijeet Singh
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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 central element

join and split

The join method combines an array into a string using a specifeid 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. Basically 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 array using slice(begin, end).

This method does not modify the array, it just copies a slice of it.

Example