基础知识

一、The differencs between JavaScript and classic OO language 

  There is a difference between JavaScript and the "classic" OO languages like c++ and Java.You should understand right form the start that in JavaScript there are no classes; everything is based on objects.

   In classic OO language: "create me a new object called Bob which is of class Person"

   In a prototypal OO language: "I am going to take this object Person that I have lying around and reuse it as a prototype for a new object that i will call Bob" .

二、Primitive date types

    。There are five primitive date types in JavaScript

       .  number(it contains positive and negative integers or floats/hex/oct/exponents/NaN/Infinity/-Infinity)

       .  string(it contains charactere)

       .  boolean(only contains true and false)

       .  undefined(the values that have been defined but not been initialized or the value that doesn't exist)

       .  null(the value is null)

  。 Everything that is not a primiary is an object

三、For in

  This loop just like for each that in Java language.

 EXP:var s = "happyjlq";

    for(var args in s){

      console.log(s[args]);

}

四、Comments

 Some examples:

  //beginning of the line

    var s = 234;// anywhere in the line

 /*multi-line comment on a single line*/

/*

   comment

   several lines

*/

五、operators

Arithmetic operators:  +, -, *, /, and %.
Increment operators:  ++ and --.
Assignment operators:  =, +=, -=, *=, /=, and %=.
Special operators:  typeof and delete.
Logical operators:  &&, ||, and !.
Comparison operators:  ==, ===, !=, !==, <, >, >=, and <=.