global variables

var d = document;
var f = d.forms[0];

function doSomething() {
f.style.marginRight = "3em";
}


That function is retarded, but the point is to illustrate what I tried to setup global variables that I reuse frequently in scripts, but it doesn't seem to work. I read that all variables are global in JS unless declared within a function, in which case they are local to that function. So what is wrong with the above then?

Because you are trying to reference an element (forms[0]) which is not yet present on the page.....

BTW: It is better to keep all variables local in scope if at all possible and with experience, it is indeed possible.....

Ah, dur, of course!

However, why is it better (aside from fixing idiotic coder error) to keep variables local? Why even have globals then?

A few reasons using local variables are better than using global variables are:

1] Up to 26x's faster than using global variables
2] Have less chance of conflicts with other scripts
3] Do not fill memory with garbage often not removed

You can also look here (http://www.codingforums.com/showthread.php?s=&threadid=33161) for a discussion on such matters.

Interesting. Thanks!