Limiting character usage

[GundamSV7]

How do you limit usage of certain characters? for example, I have a sign-up script and I want to make sure their username is only alphanumeric, no weird symbols or plus signs or anything. How would this be done?

[PallaviDalvi]

<input type=textbox id=txt name=txt onkeypress=limit();>

function limit()
{
	if(window.event.keyCode <= 97 || window.event.keyCode >= 122 )
	{
		alert ("Only small case alphabets allowed.");
		window.event.keyCode=0;
	}
}

the above code restricts the usage of any characters other than the small case alphabets. u can work on this to achieve ur goal.

[GundamSV7]

How would i allow upper case characters too?

[PallaviDalvi]

find out the keycodes for the characters u need to allow/restrict and program accordingly.