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Hybrid constructor/prototype paradigm

Car.prototype.color = “red”;

Car.prototype.doors = 4;

Car.prototype.mpg = 23;

Car.prototype.drivers = new Array(“Mike”, “Sue”);

Car.prototype.showColor = function () {

alert(this.color);

};

var oCar1 = new Car();

var oCar2 = new Car();

oCar1.drivers.push(“Matt”);

alert(oCar1.drivers); //outputs “Mike,Sue,Matt”

alert(oCar2.drivers); //outputs “Mike,Sue,Matt”

Here, a property called

drivers

is a pointer to an

Array

containing two names,

Mike

and

Sue

. Because

drivers

is a reference value, both instances of

Car

point to the same array. This means that when

“Matt”

is added to

car1.drivers

, it is also reflected in

car2.drivers

. Outputting either one of these

pointers results in the string

“Mike,Sue,Matt”

being displayed.

With so many problems in creating objects, you must be wondering if there is any way to create objects

in a rational way. The answer is to combine the best of both constructor and prototype paradigms.

Hybrid constructor/prototype paradigm

By using both the constructor and prototype paradigms, you can create an object just as you would

when using other programming languages. The concept is very simple: Use the constructor paradigm

to define all nonfunction properties of the object and use the prototype paradigm to define the function

properties (methods) of the object. The result is that functions are only created once, but each object can

have its own instance of object properties. If you once again rewrite this example, the code becomes the

following:

function Car(sColor, iDoors, iMpg) {

this.color = sColor;

this.doors = iDoors;

this.mpg = iMpg;

this.drivers = new Array(“Mike”, “Sue”);

}

Car.prototype.showColor = function () {

alert(this.color);

};

var oCar1 = new Car(“red”, 4, 23);

var oCar2 = new Car(“blue”, 3, 25);

oCar1.drivers.push(“Matt”);

alert(oCar1.drivers); //outputs “Mike,Sue,Matt”

alert(oCar2.drivers); //outputs “Mike,Sue”

Chapter 3

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