这些摘要之间有什么区别？

Question

New to javascript, I face many problems.

I read the javascript tutorial at w3cschools.com, and there are many question marks on my head.

I do not understand what is the difference below:

var name=something;

name=something;

The above two examples also giving something to a name, why 2 different ways?

name=new Array();

name[0]=something0;

name[1]=something1;

is this same with switch?

//switch start

var name=something();

switch(something)

{

case 1:

do something;

break;

case 2:

do something;

break;

default:

do something;

}

//if...else start

var name=something();

if (condition) 

{

do something

};

else if (condition)

{

do something

};

else

{

do something

};

what is the different between switch case and else.if ?

i think both 2 is doing the same thing?match condition and then do something?

and the for Loops,while Loops and break Loops ,

both 3 are doing the same thing,but 3 different ways.

can someone tell me what is the different between them?it make me confuse.

and please intro more tutorial for javascript.

many thanks here

Answer 1

For your first question, when u use "var", it defines a local scope to the variable. When you use variables without keywork "var", it means they are global variable. Usually its not a good practice to use global variables.

Also on other IF ELSE parts, you cant have semicolon before ELSE IF block.

Check these links -

Read all articles under JavaScript: http://www.crockford.com/

JavaScript: Scoping and Hoisting: http://www.adequatelygood.com/2010/2/JavaScript-Scoping-and-Hoisting

JavaScript: Function expressions vs. Function declarations vs. Function statements: http://yura.thinkweb2.com/named-function-expressions/

Answer 2

In answer to your first question:

var name=something;

name=something;

var name

This snippet creates a new variable, called name. It will be refered to in the rest of your code as name, it has been declared.

var name = something

This piece of code assumes that there is a variable declared above it called 'something', and it creates the name variable and assigns it the value of whatever 'soemething' holds at that particular point.

name = something

Without the intitial creation of the variable, this line assumes that the variable has already been declared previously, it is simply assigning that variable the value or something.

Reading

I recommend you read this webpage which appears to have a great introduction to javascript and will answer many more of your questions.

Answer 3

and a quick, easy answer to your switch question. switch is just often cleaner and more readable than a repeated else if block.
You can also do cool stuff like regular expressions in your case (case /awesome|radical/: ...). You will appreciate that later ;)