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methods

which returns only the last item,

“yellow”

, and stores it in the variable

vItem

. The array is then left

with only the strings

“red”

and

“green”

The

push()

method is actually the same as manually adding the array items as shown in previous

examples. This example could be rewritten as the following:

var stack = new Array;

stack[0] = “red”;

stack[1] = “green”;

stack[2] = “yellow”;

alert(stack.toString()); //outputs “red,green,yellow”

var vItem = stack.pop();

alert(vItem); //outputs “yellow”

alert(stack.toString()); //outputs “red,green”

The

Array

also provides methods to manipulate the very first item. The

shift()

method removes the first

item in the array and returns it as the function value. On the other end of the spectrum, the

unshift()

method places an item into the first position of the array, shifting all other items down one position in the

process. Example:

var aColors = [“red”, “green”, “yellow”];

var vItem = aColors.shift();

alert(aColors.toString()); //outputs “green,yellow”

alert(vItem); //outputs “red”

aColors.unshift(“black”);

alert(aColors.toString()); //outputs “black,green,yellow”

In this example, the string

“red”

is removed (

shift()

ed) from the array, leaving only

“green”

and

“yellow”

. By using the

unshift()

method, the string

“black”

is placed at the front of the array, effec-

tively replacing

“red”

as the new value in the first position.

By using

shift()

and

push()

, it is possible to make an

Array

object behave like a queue. A queue is a

member of the group of data structures that restricts the insertion and removal of elements. A queue is

referred to as a

last-in-last-out

(LILO) structure, meaning that the most recently added element is the last

one removed. The insertion of elements always occurs only at the back of the queue whereas the

removal of elements occurs only at the front of the queue.

When you think of a queue, think of a line at the movies. When new people arrive to get tickets, they go

to the back of the line (Figure 3-3). This is traditionally called

put

enqueue

Figure 3-3

12345

1234

Star t

Put

Result

Object Basics

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