javascript var

[Andy Hahn]

I can't find the answer to this question anywhere!

Can someone tell me when it is applicable to use the "var" keyword and when is it not? Or does the scope of the variable make a difference?

Is var supposed to be used for Strings only? What about Integers, Dates, etc?

Most of the advanced javascript functions I have been reviewing do not use var anywhere.

Thanks!!

[Eric Pascarello]

run this code:

var a = "1";
function test(){
 a += 1;
 b = parseInt("12 apples");
 var c = 123;
}
alert("a: " + typeof a);
alert("b: " + typeof b);
alert("c: " + typeof c);
test();
alert("a: " + typeof a);
alert("b: " + typeof b);
alert("c: " + typeof c);

I do this code when I do my talks. See if you can see what happens when you do not use var.

Eric

[Eric Pascarello]

If you want to see how to code JavaScript better read an exerpt from my book: http://java.sun.com/javascript/ajaxinaction/Ajax_in_Action_ApB.html

Eric

[Bear Bibeault]

Place the following script fragment into an html page and display it.

<script>
var xyz = 1;
xyz = 2;
alert(xyz);
alert(window.xyz);
 
function abc() {
  var xyz = 3;
  alert(xyz);
  alert(window.xyz);
}
 
abc();
</script>

What do you conclude from the results?

[Bear Bibeault]

BONK!

[Andy Hahn]

So the keyword "var" declares the variable, and if I declare the variable at the global level and at the function level, they will be treated as two separate refrences? Is that correct?

So is it true that I do not have to use the "var" keyword if I want to declare a variable only at the global level?

[Eric Pascarello]

Delcare your variables and use semicolons. If you don't, it leads to sloppy coding and that leads to problems.

Eric
[ June 15, 2006: Message edited by: Eric Pascarello ]

[Bear Bibeault]

Originally posted by Andy Hahn:

So is it true that I do not have to use the "var" keyword if I want to declare a variable only at the global level?

Essentially, but it is considered poor practice.

At global level, whether you use the var keyword to declare a variable, or cause it to be automatically created by assigning a value to a previously undeclared variable, it still ends up as a property on the window object.

Not declaring the variable is sloppy and I'd avoid it.