global variable problem

[BaronZ]

if(true){
	var a = 2;//i thought 'a' is a local variable here.
}
alert(a);//but here it pops up '2',which means 'a' is a global variable?why?

[Philip M]

Why do you think that a is global? If your code is within a function then a is local, and alert (a) results in the value of a being alerted.

<script type="text/javascript">

test();

var a = 10;
function test() {
var a = 12;  // note the var keyword defines a new variable local to the function.  But it is obviously silly to duplicate names in this way.
alert ("Local " + a);  //12
}
alert ("Global " + a); //10

</script>

if(true) is meaningless as the condition will always be true.

All advice is supplied packaged by intellectual weight, and not by volume. Contents may settle slightly in transit.

[BaronZ]

Originally Posted by Philip M

Why do you think that a is global? If your code is within a function then a is local, and alert (a) results in the value of a being alerted.

<script type="text/javascript">

var a =10;
function test() {
var a = 12;
alert ("Local " + a);  //12
}
alert ("Global " + a); //10

test();

</script>

if(true) is meaningless as the condition will always be true.

All advice is supplied packaged by intellectual weight, and not by volume. Contents may settle slightly in transit.

umm,but if a is not global,why the alert box shows '2'?

[Philip M]

Originally Posted by BaronZ

umm,but if a is not global,why the alert box shows '2'?

I think you need to better understand global and local scope. You seem to be unclear. Study the example I have given you.

http://stackoverflow.com/questions/5...variable-scope

<script type="text/javascript">

test();

var a = 10;
function test(){ 
if(true) { 
var a = 40; 
} 
alert (a); // within the function alerts '40', not the global value of '10' 
} 
alert (a);  // outside the function alerts global value of '10'

</script>

[BaronZ]

i understand the example u showed me.but in the code i showed above,i think 'a' is a local variable,so in my opinion,alert(a) should pop up 'undefined' or sth,but it's '2',that's what confused me.

[Philip M]

Originally Posted by BaronZ

i understand the example u showed me.but in the code i showed above,i think 'a' is a local variable,so in my opinion,alert(a) should pop up 'undefined' or sth,but it's '2',that's what confused me.

If your code fragment is not contained within a function then the variable a is global scope. Do what I say - study the topic.

[BaronZ]

Originally Posted by Philip M

If your code fragment is not contained within a function then the variable a is global scope. Do what I say - study the topic.

ic now

[BaronZ]

kinda different from java

[Philip M]

Originally Posted by BaronZ

kinda different from java

Java and Javascript are entirely different programming languages, in spite of the confusingly similar names. Rather like Austria and Australia!