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dynamic prototyping

}

Rectangle.prototype = new Polygon();

Rectangle.prototype.getArea = function () {

return this.length * this.width;

};

Notice that the

Rectangle

constructor also doesn’t accept

sides

as an argument, and once again a con-

stant value (

) is passed directly to the

Polygon

constructor. Also similar to

Triangle

Rectangle

introduces two new properties as arguments to the constructor and then overrides the

getArea()

method.

Testing the code

You can test the code created for this example by running the following code:

var triangle = new Triangle(12, 4);

var rectangle = new Rectangle(22, 10);

alert(triangle.sides); //outputs “3”

alert(triangle.getArea()); //outputs “24”

alert(rectangle.sides); //outputs “4”

alert(rectangle.getArea()); //outputs “220”

This code creates a triangle, with a base of

and a height of

, and a rectangle, with a length of

and

a width of

. Then, both the number of sides and the area of each shape are output to prove that the

sides

property is being properly filled and the

getArea()

method is returning the correct value. The

area of the triangle should be

and the area of the rectangle should be

220

What about dynamic prototyping?

The previous example uses the hybrid constructor/prototype paradigm of object definition to show

inheritance, but does it work with dynamic prototyping? The answer is no.

The reason that inheritance doesn’t work with dynamic prototyping is because of the unique nature of

the

prototype

object. Take a look at the following code (which is incorrect, but important to study

nonetheless):

function Polygon(iSides) {

this.sides = iSides;

if (typeof Polygon._initialized == “undefined”) {

Polygon.prototype.getArea = function () {

return 0;

};

Polygon._initialized = true;

}

function Triangle(iBase, iHeight) {

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