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Classification of objects:
- User
Defined objects
- Javascript
native objects
User defined objects:
- According to user
needs objects can be customized by users,such objects are called as
user-defined objects.
- All user-defined objects and built-in objects are descendants of an object called Object.
·
The new operator is used to create an instance of an object.
·
To create an object, the newoperator is followed by the constructor method.
Example:
The
constructor methods are Object(), Array(), and Date(). These constructors are
built-in JavaScript functions.
var employee = new Object();
var books = new Array("C++",
"Perl", "Java");
var day =
new Date("october 17, 1947");
The Object() Constructor:
·
A constructor is a function
that creates and initializes an object.
·
JavaScript provides a special
constructor function called Object() to build the object.
·
The return value of the
Object() constructor is assigned to a variable.
·
The variable contains a
reference to the new object. The properties assigned to the object are not
variables and are not defined with the var keyword.
example
demonstrates how to
create an object:
<html>
<head>
<title>User-defined
objects</title>
<script
type="text/javascript">
var book = new
Object(); // Create the object
book.subject = "programming in c";
// Assign properties to the object
book.author
= "Balagurusamy";
</script>
</head>
<body>
<script
type="text/javascript">
document.write("Book name is : " +
book.subject + "<br>");
document.write("Book author is : "
+ book.author + "<br>");
</script>
</body>
</html>
example
demonstrates how to
create an object with a User-Defined Function. Here thiskeyword is used to refer
to the object that has been passed to a function:
<html>
<head>
<title>User-defined
objects</title>
<script
type="text/javascript">
function book(title,
author){
this.title = title;
this.author
= author;
}
</script>
</head>
<body>
<script
type="text/javascript">
var myBook = new book("Programming in C",
"Balagurusamy");
document.write("Book title is : "
+ myBook.title + "<br>");
document.write("Book author is : "
+ myBook.author + "<br>");
</script>
</body>
</html>
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