 Using the prototype object to add custom properties to objects
The prototype object is here to help when you wish to
quickly add a custom property to an object that is reflected on all
instances of it. To use this object, simply reference the keyword
"prototype" on the object before adding the custom property to it, and this
property is instantly attached to all instances of the object. A
demonstration is worth a thousand words, so I'll show one right now: Let's
define the custom property "pi" in the above in a way so it's a default
property of all instances of circle():
//First, create the custom object "circle"
function circle(){
}
circle.prototype.pi=3.14159
Having done the above, all instances of circle() now has the
pi property prebuilt into them.
There is an important thing to take note at this point in
the tutorial. While you are free to use the prototype object on any custom
objects, this is NOT the case with prebuilt ones (such as
image, string
etc). JavaScript only allows you to "prototype" prebuilt objects that are
created with the new keyword, such as the
following:
- The image object
- The string object
- The date object
- The Array object
In the final part of this tutorial, I'll demonstrate an example involving
prototyping a prebuilt JavaScript object.
Let's move on to see how to use the prototype object to add custom
methods.
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