Essentials of Javascript - Cultural View

JavaScript syntax 39
Constructors
Constructor functions simply assign values to slots of a newly created object. The values may be data or other
functions.
Example: Manipulating an object
function MyObject(attributeA, attributeB) {
}
this.attributeA = attributeA;
this.attributeB = attributeB;
MyObject.staticC = "blue"; // On MyObject Function, not obj
alert(MyObject.staticC); // blue
obj = new MyObject('red', 1000);
alert(obj.attributeA); // red
alert(obj["attributeB"]); // 1000
alert(obj.staticC); // undefined
obj.attributeC = new Date(); // add a new property
delete obj.attributeB; // remove a property of obj
alert(obj.attributeB); // undefined
delete obj; // remove the whole Object (rarely used)
alert(obj.attributeA); // throws an exception
The constructor itself is stored in the special slot constructor. So
x = new Foo()
// Above is almost equivalent to
y = {};
y.constructor = Foo;
y.constructor();
// except
x.constructor == y.constructor // true
x instanceof Foo // true
y instanceof Foo // false, surprisingly.
Functions are objects themselves, which can be used to produce an effect similar to "static properties" (using
C++/Java terminology) as shown below. (The function object also has a special prototype property, as discussed in
the Inheritance section below.)
Object deletion is rarely used as the scripting engine will garbage collect objects that are no longer being referenced.