Using the index, you can also update the values of the 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 don't exist and return the undefined value if accessed. Check out this example:

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

To delete an element, you use the delete operator. However, after the deletion, the length of the array does not change. In a sense, you get a hole in the array:

> var a = [1, 2, 3];
> delete a[1];
true
> a;
[1, undefined, 3]
> typeof a[1];
"undefined"

Arrays can contain all types 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, Array[3]]

The Array[3] in the result is clickable in the console and it expands the array values. Let's see an example where you have an array of two elements, both of them being other arrays:

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

The first element of the array is a[0], and it's also an array:

> 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 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 you'll get to those in Chapter 4, Objects), but let's stop here for now, remembering that: