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The prototype object of JavaScript

No, we're not going to discuss how to construct a new version of JavaScript in this tutorial. The prototype object of JavaScript, introduced starting in JavaScript 1.1, is a prebuilt object that simplifies the process of adding custom properties/ methods to all instances of an object. I know, I'm starting to sound a little geeky already, but hay, JavaScript isn't just about fun and games...it's important to learn the serious side of it too.

A little background first...

In JavaScript, you're allowed to add custom properties to both prebuilt and custom objects. Here's an example of each:

//adding a custom property to a prebuilt object
var myimage=new Image()
myimage.size="26k"

/*adding a custom property to the custom object "circle"*/
//First, create the custom object "circle"
function circle(){
}
var smallcircle=new circle()
smallcircle.pi=3.14159

A custom property added this way only exists for that instance of the object. If I were to spit out another instance of circle(), called "bigcircle", for example, bigcircle.pi would by default return "undefined" until I go over the process again of first defining bigcircle.pi, as with smallcircle.

There are times when you'll want to add a custom property that's only reflected on a particular instance of an object, and times, when you just wished all instances of the object would  recognize the custom property already. For example, all circles- and not just small circles- have a pi, so it's reasonable to assume you'd like the custom property "pi" added in a way so that it's default across all instances of the circle object. That's where the prototype object of JavaScript comes in.

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