Javascript Reference Guide

 
 
This guide contains useful Javascript tips.

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Create javascript objects.



Information



Examples
<script type="text/javascript" language="JavaScript">

// 1. Create a Car 'class', using the function keyword.
//    This function is also called the "constructor function"
function Car(type, wheels, doors, color, maxspeed) {
   this.type = type;
   this.doors = doors;
   this.color = color;
   this.wheels = wheels;
   this.maxspeed = maxspeed;
}

// 2. Assign methods to the Car 'class' using the prototype keyword.
//    With the prototype keyword you can add properties and methods
//    The prototype property allows you to specify object properties 
//    outside the constructor function, which will be shared by all 
//    the objects instantiated from this function.
Car.prototype.changeMaxSpeed = function(maxspeed) {
    this.maxspeed = maxspeed;
}
Car.prototype.changeColor = function(color) {
    this.color = color;
}

// 3. Create a helper function
function showObjProp(obj) {
    var str='';
    for(var i in obj){
        if(i=="type" || i=="doors" || i=="color" || i=="wheels" || 
           i=="maxspeed" || i=="fuel") {
           str += i+" = "+obj[i]+"\n";
        }
    }
    alert(str);
}

// 4. Create mycar object by calling its constructor
mycar = new Car("limousine", 6, 4, "white", 60);
showObjProp(mycar);

// 5. Access mycar properties/methods using the dot operator 
if(mycar.wheels == 6) {
    mycar.changeMaxSpeed(100);
    mycar.changeColor("red");
    showObjProp(mycar);
}

// 6. Define a Truck 'class', the arguments must match the Car 'class'
function Truck(type, wheels, doors, color, maxspeed) {
    this.type = type;
    this.doors = doors;
    this.color = color;
    this.wheels = wheels;
    this.maxspeed = maxspeed;
}

// 7. The Truck is a subclass of Car
Truck.prototype = new Car();

// 8. Add additional properties and methods to the Truck 'class'
Truck.prototype.fuel = "gas";
Truck.prototype.changeFuel = function(fuel) {
    this.fuel = fuel;
}

// 9. Correct the constructor pointer because it points to Car
Truck.prototype.constructor = Truck; 
 
// 10. Create a mytruck object by calling its constructor
mytruck = new Truck("truck", 8, 2, "black", 60);
showObjProp(mytruck);

// 11. Access mytruck methods using the dot operator 
mytruck.changeMaxSpeed(200);
mytruck.changeFuel("diesel");
showObjProp(mytruck);
</script>
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