//限制文本框输入字数
function OnFeedbackChange(field, maxLength, counter)
{ 
	try
	{
		var counterSpan = document.getElementById(counter);
		var textBox = document.getElementById(field);
		var length;

		if(typeof(textBox) != "undefined") length = textBox.value.length;

		if(typeof(length) != "undefined")
		{
			var charsRemaining = maxLength - length;
			var scrolltop = textBox.scrollTop;
			var scrollleft = textBox.scrollLeft;
			if(charsRemaining < 0) 
			{ 
				textBox.value = textBox.value.substring(0, maxLength);
				charsRemaining = 0 
				textBox.scrollTop = scrolltop;
				textBox.scrollLeft = scrollleft;
			}
			counterSpan.innerHTML = charsRemaining;
		}
	}
	catch(e){}
}