HTML and CSS Reference
In-Depth Information
EXPLANATION
1
An
Array
object is declared.
2
The
length
property is used to get the length of the array. The length is 6.
3
The
book
is an
Array
object created by the
Array()
constructor. The
constructor
property shows that this is native (primitive) code and the name of the construc-
tor function is
Array()
.
4
The
book
array object is set to a length of 0, meaning all elements with an index
of 0 or more will be removed from the array, leaving an empty array. If you set the
length to 2, all values with index value of 2 or more will be removed.
5
The value is
undefined.
It was removed by setting the length of the array to 0.
6
All the elements of the array have been removed; its length is now 0. Figure 9.7
shows the output.
Figure 9.7
Array properties.
JavaScript allows use of a string value as an index of an array. An array that uses a string
as an index value instead of a number is called an associative array. There is an associa-
tion between the index and the value stored at that location. The index is often called a
key
and the value assigned to it, the
value
. Key/value pairs are a common way of storing
and accessing data. In the following array called
states
, there is an association between
the value of the index, the abbreviation for a state (e.g.,
“CA”
), and the value stored
there—the name of the state (e.g.,
“California”
). The special
for
loop can also be used to
iterate through the elements of an associative array. We will see many examples through-
out the rest of the text where associative arrays are used.
1
1. This type of array has nothing to do with the built-in Array object. Saying object[“property”] is just
another way of saying object.property. It's another way of representing an object's property. This means
that the Array object's
length
property is not used with associative arrays, nor do the
Array
methods apply,
which are covered later in this chapter.
