Implement program flow - Programming in HTML5 with JavaScript and CSS3 - page 121

Implementing special types of arrays
JavaScript doesn't natively provide a custom object to represent specialized collections or
arrays. Instead, methods are provided on the Array object that allows you to implement
various types of specialized collections such as a queue or a stack.
A queue is essentially a first-in-first-out type of collection. Whenever items are added to
the list, they should go at the end of the line. In contrast, a is a last-in-first-out type of collec-
tion in which the last item put on the stack is the first item you can take out of the stack. The
array methods that facilitate this type of behavior are pop , push , shift , and unshift .
Using the pop and push methods
The pop and push methods provide stack functionality. The push method appends the speci-
fied items to the end of the array. The pop method removes the last item from the array. The
following code demonstrates the push method:
var sports = new Array();
sports.push('soccer', 'basketball', 'hockey');
sports.push('football');
This code creates an Array object, and then inserts (pushes) three items into the array.
The items are added to the stack in the same order in which they appear in the parameter
list. Next, the code pushes one additional item onto the stack. The pop method removes and
returns the last item in the array:
var nextSport = sports.pop();
When this code runs, the nextSport variable holds the value 'football' because that was the
last value added to the array.
NOTE USING PUSH AND POP ON ANY ARRAY
You can use the pop and push methods in any context to add and remove items from the
end of an array. The stack concept is useful but isn't a confining mechanism that limits use
of these methods to just stack arrays.
Using the shift and unshift methods
The shift and unshift methods work in the exact opposite way from the pop and push
methods. The shift method removes and returns the first element of the array, whereas the
unshift method inserts new elements at the beginning of the array. The following code uses
the shift and unshift methods:
var sports = new Array();
sports.unshift('soccer', 'basketball', 'hockey');
sports.unshift('football');
var nextSport = sports.shift();