Validate Keystrokes

[blasterstudios]

I want to validate keystrokes and only allow lowercase letters, numbers, underscore, and dash. No spaces, no capital letters, and no special characters or symbols. I want it to check my form on the fly as well. So like on the onKeyPress event, it checks it. How do i go about doing this?

Here's what I tried, but it doesn't work:

function letternumber(e)
{
var key;
var keychar;

if (window.event){
   key = window.event.keyCode;
else if (e)
   key = e.which;
}

if ((key==null) ||
	((key>=97) && (key<=122)) ||
	((key>=48) && (key<=57)) ||
	(key==95) || (key==45) || (key==97))
   return true;
else
   return false;
}

 

[tsuji]

[tt]>if (window.event){
> key = window.event.keyCode;
>else if (e)
> key = e.which;
>}
[/tt][tt]
if (window.event){
key = window.event.keyCode;
[red]}[/red]
else if (e)
[red]{[/red]
key = e.which;
}
[/tt]