4. JavaScript

First, the concept of javascript: is based on object and event scripting language .

1. Features:

a), security.

b), cross-platform (as long as the browser can interpret JS can be executed, and platform-independent)

2. The difference between JavaScript and Java:

A), JS is Netscape company products, Java is Oracle Company
b), JS is an object-based, Java is object-oriented
c), JS can be executed simply by explanation, Java needs to be compiled into a bytecode file before execution
d), JS is a weak type, Java is a strong type

3, the combination of JavaScript and HTML:

A), JS code stored in the label <script>...</script>
b), using the SRC attribute of the script tag to introduce a JS file (<script type= "Text/javascript" src= "js file" ></script>)

Second, JavaScript syntax:

1.variables：defined by the keyword Var, the weak type does not need to specify a specific data type(Note: JS in the special constant value undefined, when the variable is not initialized to be used, the value of the variable is undefined)
var V;
v = v + 5;
Alert (v);//result is Nan
2. Statement (same as Java statement format): logical operator:&& | |
If statement:
Note: var x = 3;
if (x==4)//can perform comparison operations
if (x=4)//can be assigned to the operation, but also can be judged
Reason: In JS0 can indicate false, not 0 can represent true (usually 1), so the IF (x=4) result is true.non-null is true,null to False
Switch statement: switch (x), where x can receive a string
Loop statement (while\do...while\for)
For (variable in object) {...}
3. Function:
General functions:Format: Function name (formal parameter ...) {...}
Note: When you call a function that has parameters, but you do not give it a value, the function can run, or you can call a function that has no parameters and pass a value to it.
There is a parameter array object (arguments) in the function that encapsulates the passed parameters in an array
When you define a variable in a function without using the var keyword, the variable becomes a global variable after executing the function.
The function is written at the time of invocation:
var s = method ();//s variable receives the return value of the method function
var s = method;//s and method represent the same function, then the function can also be called by means of S ()
　　　　 Anonymous Functions: Format: function () {...} (or simply pass the function directly as a parameter, without encapsulation)
Example: var demo = function () {...}
Call: Demo ();
4.Array：
　　　　 Features: The length is variable, can save any element (array of elements can be stored in different types)
Definition Format: var arr = new Array ();
Arr[0] = "Hello";
ARR[1] = 1;
ARR[2] = true;

Output: var arr = ["123", at +, true];

4. JavaScript