JavaScript Object-Oriented Concept Essential Part1

1. Everything excpet primitive types in JavaScript is object.
2. Primitive types include Undefined, Null, Boolean, Number and String.
3. JavaScript has three kinds of objects.

• 3.1 Build-in objects: Array, Image, Date...

• 3.2 Host objects: window, document, forms..

• 3.3 User-defined.

4. Primitive types has associated object.

• Ex, var stringObj = new String("create String object");

5. new is used to create objects.
6. this is used to refer the current object.
7. class in Javascript is defiend as function.

• class field and function is defined by this. Ex,
• function Cicle(radius){
• this. radius = radius; // defined class field, assigned by parameter of constructor
• this. getArea = getArea; // defined class function, getArea is a function
• function getArea(){return this. radius;}// still use this to refer current object
• //the function getArea can also be defiend outside the class, with this. radius always
• //refer the object who use the funtion.

• }

8. Many ways to define a function, and whenever you create a function, you create a object of the function

• 8.1 functionName = function("para1","para2");// the last para is the body of the //function, you can use the functionName as the callable block, and it is an object
• 8.2 var myFunctionObj = new Function();
• 8.3 var myFunctionObj = Function();
• 8.4 var myFunctionObj = function(){};
• 8.5 function myFunctionObj(){};

9. A variable can not have field. Only object can have.
Ex, var primitiveString = "I am string varible" ;
primitiveString.prop = "my property"; // this is wrong

While var stringObj = new String("make a string object");
stringObj.prop = "my property"; //this is correct