Javascript onkeup() function that prevents entering more than X characters

chars_remaining.js

function charsRemaining(evt, counterID, max) {
	var chars = evt.getValue();
	if (chars.length == 1 && chars[0] == '') { chars = []; }
	var remaining = max - chars.length;
	var counter = document.getElementById(counterID);
	if (remaining >= 0) {
		if(counter) counter.setTextValue(remaining + ' characters remaining');
	}
	else {
		evt.setValue(evt.getValue().substr(0, max));
		if(counter) counter.setTextValue((remaining * -1) + ' characters over');
	}
}