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javascript prototype

Posted on 2015-01-09
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Last Modified: 2015-01-09
Hello expert,

Working on learning about using inheritance in JavaScript
through the prototype property. Looking at some code at
http://www.javascriptkit.com/javatutors/proto3.shtml

This code is offered at the tutorial
++++++++begin code+++++++++++++++
//First, create the custom object "circle"
function circle(){
}
circle.prototype.pi=3.14159

// create the object method
function alertmessage(){
alert(this.pi)
}
circle.prototype.alertpi=alertmessage

++++++++end code+++++++++++++++

So I put it in an HTML page in <script> tags.
Complete page copied herewith below.
But the page did not do anything. Then I realized
that the function had to be called so I
called the function with the onLoad event
in the body tag.

This ran the function but returned 'undefined'.
When JavaScript returns 'undefined ' that
usually means that the variable had not
declared. So looking at the code the
object 'alertpi' does not seem to be defined
so I tried
'circle.prototype.alert=alertmessage'
But still no luck.

Any idea how to make the script work?

Thanks.

Allen in Dallas






++++++++++++++begin page+++++++++++++++++
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
<HTML>
<HEAD>
<TITLE>JS_prototype</TITLE>

<STYLE>
BODY {font-family: Arial;}
</STYLE>

</HEAD>

<body onLoad=alertmessage()>

<h1>Prototype property</h1>

<script>

//First, create the custom object "circle"
function circle(){
}
circle.prototype.pi=3.14159

// create the object method
function alertmessage(){
alert(this.pi)
}
circle.prototype.alertpi=alertmessage

</script>

</BODY>
</HTML>
++++++++++++++end page++++++++++++++++++++
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Question by:Allen Pitts
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2 Comments
 
LVL 44

Accepted Solution

by:
Rainer Jeschor earned 2000 total points
ID: 40540747
Hi,
you will have to create the object and use the alertpi property/function like here
http://jsfiddle.net/66rmhwab/

HTH
Rainer
0
 

Author Closing Comment

by:Allen Pitts
ID: 40540764
Well done Rainer.
0

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