var prevLength = 0;

function updateCharsRemaining(input, maxLength)
{
	var newLength = input.value.length;
	input.value = input.value.substr(0, maxLength);
	var charsRemaining = maxLength - input.value.length;
	document.getElementById('charsremaining').innerHTML = charsRemaining;
	if (newLength > maxLength && newLength > prevLength) alert('Maximum length exceeded!');
	prevLength = input.value.length;
}