Adding/Updating Array Elements

Using the index, you can also update elements of the array. The next example updates the third element (index 2) and prints the contents of the new array.

>>> a[2] = 'three'; 

"three"

>>> a 

[1, 2, "three"]

You can add more elements, by addressing an index that didn't exist before.

>>> a[3] = 'four'; 

"four"

>>> a 

[1, 2, "three", "four"]

If you add a new element, but leave a gap in the array, those elements in between are all assigned the undefined value. Check out this example:

>>> var a = [1,2,3];
>>> a[6] = 'new';

"new"

>>> a

[1, 2, 3, undefined, undefined, undefined, "new"]

Deleting Elements

In order to delete an element, you can use the delete operator. It doesn't actually remove the element, but sets its value to undefined. After the deletion, the length of the array does not change.

>>> var a = [1, 2, 3];
>>> delete a[1];

true

>>> a

[1, undefined, 3]

Arrays of arrays

An array can contain any type of values, including other arrays.

>>> var a = [1, "two", false, null, undefined]; 
>>> a 

[1, "two", false, null, undefined]

>>> a[5] = [1,2,3] 

[1, 2, 3]

>>> a 

[1, "two", false, null, undefined, [1, 2, 3]]

Let's see an example where you have an array of two elements, each of them being an array.

>>> var a = [[1,2,3],[4,5,6]]; 
>>> a 

[[1, 2, 3], [4, 5, 6]]

The first element of the array is a[0] and it is an array itself.

>>> a[0] 

[1, 2, 3]

To access an element in the nested array, you refer to the element index in another set of square brackets.

>>> a[0][0] 

1

>>> a[1][2] 

6

Note also that you can use the array notation to access individual characters inside a string.

>>> var s = 'one';
>>> s[0]

"o"

>>> s[1]

"n"

>>> s[2]

"e"

There are more ways to have fun with arrays (and we'll get to that in Chapter 4), but let's stop here for now, remembering that: