function fmt(obj) {
			if(!isNum(obj.value)&&obj.value!=""){
				obj.value = "";
				showMsgPanel("<font style='color:red;'>請輸入數字！</font>", "系統提示");
			}
			else{
				var vb = obj.value;
				obj.value = fmtValue(vb);
			}
		}
		
		function unfmt(obj) {
			obj.value = obj.value.replace(/\,/g, "");
			obj.select();
			return obj.value;
		}
		
		function isNum(num){
			if(/^\d+(\.\d+)?$/.test(num)){
				return true;
			}
			return false;
		}
		
		function fmtValue(value) {
			var vb = value.split('.');
			var val = vb[0].replace(/\D/g, '');
			if (vb.length > 0) {
				var len = val.length;
				var fir = len % 3;
				var sb = [];
				if (len > 3) {
					if (fir > 0) {
						sb[sb.length] = val.substring(0, fir) + ",";
					}
					for (var i = fir + 3; i <= len; i += 3) {
						sb[sb.length] = val.substring(i - 3, i) + ",";
					}
					var end = sb[sb.length - 1];
					sb[sb.length - 1] = end.substring(0, end.length - 1);
				} else {
					sb[sb.length] = val;
				}
				return sb.join("")
						+ (vb.length > 1 ? (vb[1].length > 0 ? '.' + vb[1].substring(0,3) : ''): (vb[0].length > 0 ? '.000' : ''));
			}
			return "";
		}
 

一個輸入框

<input name="custAccBal" type="text" class="textBox" style="height: 20px; 

width: 125px; border: solid 1px #6699cc; color: blue; font-weight: bolder;text-align:right" 

pattern="money"  autocheck="true" onblur="fmt(this);" onfocus="unfmt(this);">