JavaScript 2.0-The Complete Reference, Second ... - freecodingtutorial

}
this.hasJetpack = true;
This example adds an instance property hasJetpack to each new object it creates. After
creating an object with this constructor, we can access the hasJetpack property as one would
expect:
var guard = new Robot();
var canFly = guard.hasJetpack;
Since constructors are functions, you can pass arguments to constructors to specify initial
values. We can modify our constructor again so that it takes an optional argument:
function Robot(needsToFly)
{
}
if (needsToFly == true)
else
this.hasJetpack = true;
this.hasJetpack = false;
// create a Robot with hasJetpack == true
var guard = new Robot(true);
// create a Robot with hasJetpack == false
var sidekick = new Robot();
Note that in this example we could have explicitly passed in a false value when creating the
sidekick instance. However, by passing in nothing, we implicitly have done so, since the
parameter needsToFly would be undefined. Thus, the if statement fails properly.
We can also add methods to the objects we create. One way to do so is to assign an instance
variable an anonymous function inside of the constructor, just as we added an instance
property. However, this is a waste of memory because each object created would have its own
copy of the function. A better way to do this is to use the object‘s prototype.
Prototypes
Every object has a prototype property that gives it its structure. The prototype is a reference to
an Object describing the code and data that all objects of that type have in common. We can