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Functions is a set of commands used in working either . Which runs on the run.

JavaScript Functions Syntax

   Nature of the function is as follows.

function named functions (arguments) .

{ / / Commands } - function names . Naming function is similar to the principle of variable naming . By bestselling author with lowercase. Or if there are multiple words may begin with lowercase letters. The next start with a capital letter such as submitForm (), blockInvalidChar () etc..

  - Arguments (argument) , or the parameter is some information functions required in data processing. This argument is optional , depending on the need .


Running the function .

   For me to run the software function , then the function name and arguments  at the point you want to use this function . 

However, the run function , not necessarily in the same <script> tag with the writing function . Or some of the run function can be in HTML tags , but running the function in the HTML tags are mainly caused by the response to certain actions, such as clicking a check . Sainsbury, the characters , etc. 


<p>Click the button to call a function with arguments</p>
<button onclick="myFunction('Spiderman','SuperHero')">Click Here</button>
function myFunction(name,job)
{alert("Welcome " + name + ", the " + job);}

This is the result:


From the above example, when clicking the button. Appears 'welcome Spiderman the SuperHero'.


The function returns (Functions With a Return Value). 

    A function return value is created like a normal function. But before the end of the function is used to send commands return some value back out, 


<p id="demo"></p>
function myFunction(a,b)
return a*b;

This example calls a function which performs a calculation, and returns the result:

This is the result: 


It is evident that the function was being sent back. Which is that it is the answer to a multiple of a and b or 5x3 which is 15 itself. 

    To run the function with the return value. If we want to bring it up to use it to create other variable is the value returned is like.


var a = oddorEven (9); // storing the function of the variable a.
var b = oddorEven (10);


Function and scope of the variable.

  The scope of the function is defined by { } block , so the declaration or use variables. We must consider the extent of the scope of variables and functions well. 

As follows:

1 . Variables declared in a function (local variable).

Variables declared in a function , it is only available in the function . We were unable to run the variable declared in the function from outside the function , 

for example.

function f () {
var x = 123; 

document.write (x); / / Error! Error occurred because the variable x declared it in the blog function f () function, which at the end of it. Variables such it shall be canceled. We can not refer to variables such.


2. Variables that need to be shared (global variable). 

There may be some information that we need to use both in and out of functions. In this case, to create a global variable to store the data. Which variable is to build it outside the function. And not on any such function. 

var ab = 123; 
function f () {
ab + +; / / ok!,}. 
document. write (ab); // 123. 
f (); 
document. write (ab); // 124.





Chapter 10 - JavaScript Operators