JavaScript is an excellent language to write object oriented web
applications. It can support OOP because it supports inheritance through
prototyping as well as properties and methods. Many developers cast off
JS as a suitable OOP language because they are so used to the class
style of C# and Java. Many people don't realize that JavaScript
supports inheritance. When you write object-oriented code it instantly
gives you power; you can write code that can be re-used and that is
encapsulated.
Objects
work so well because they act just like real life objects- objects have
properties and methods. So if we were talking about a lamp, a property
of it may be its height or width, say 12cm. A method of it may be to
shine (an action). And when it's shining, its brightness property would
be of a greater value than when it wasn't.
JavaScript gives you the ability to make your own objects for your own applications. With your objects you can code in events that fire when you want them to, and the code is encapsulated. It can be initialized any amount of times.
There
are several ways to create objects in JavaScript, and all of them have
their place. The simplest way is to use the new operator, specifically, new Object():
Another
inline way of defining an object is via literal notation. Supported in
JavaScript1.2 and above, it's a more robust form of creating an object
on the fly:
While using the new operator or literal notion to create a custom object is both simple and logical, the biggest shortcoming is that the result is NOT reusable- we cannot easily initialize different versions of the created object. For example with the first demonstration above, if the person's name is not "Tim Scarfe", we would need to redefine our entire object just to accommodate this change.
What's so great about objects?
Objects
work so well because they act just like real life objects- objects have
properties and methods. So if we were talking about a lamp, a property
of it may be its height or width, say 12cm. A method of it may be to
shine (an action). And when it's shining, its brightness property would
be of a greater value than when it wasn't.JavaScript gives you the ability to make your own objects for your own applications. With your objects you can code in events that fire when you want them to, and the code is encapsulated. It can be initialized any amount of times.
Creating objects using new Object()
There
are several ways to create objects in JavaScript, and all of them have
their place. The simplest way is to use the new operator, specifically, new Object():<script language="javascript" type="text/javascript">
<!--
person = new Object()
person.name = "Tim Scarfe"
person.height = "6Ft"
person.run = function() {
this.state = "running"
this.speed = "4ms^-1"
}
//-->
</script>
We define a custom object "person," then add to
it its own properties and method afterwards. In this case, the custom
method merely initializes two more properties.
Creating objects using Literal Notation
Another
inline way of defining an object is via literal notation. Supported in
JavaScript1.2 and above, it's a more robust form of creating an object
on the fly:<script language="javascript" type="text/javascript">
<!--
// Object Literals
timObject = {
property1 : "Hello",
property2 : "MmmMMm",
property3 : ["mmm", 2, 3, 6, "kkk"],
method1 : function(){alert("Method had been called" + this.property1)}
};
timObject.method1();
alert(timObject.property3[2]) // will yield 3
var circle = { x : 0, y : 0, radius: 2 } // another example
// nesting is no problem.
var rectangle = {
upperLeft : { x : 2, y : 2 },
lowerRight : { x : 4, y : 4}
}
alert(rectangle.upperLeft.x) // will yield 2
//-->
</script>
Literal notion can contain arrays or arbitrary JavaScript expressions or values.While using the new operator or literal notion to create a custom object is both simple and logical, the biggest shortcoming is that the result is NOT reusable- we cannot easily initialize different versions of the created object. For example with the first demonstration above, if the person's name is not "Tim Scarfe", we would need to redefine our entire object just to accommodate this change.
0 comments:
Post a Comment