function checkDragonCode(){
	var dragonCode=document.getElementById("dragonCode").value;	
	//alert(dragonCode.length);
	if (dragonCode== ""){
		alert("卡号不能为空!"); 
		
		return (false);
	} else if(dragonCode.length!=16){
		alert("卡号位数不够!");
		return (false);
	}else if(isDigit(dragonCode)==false){
		alert("只能输入数字");
		return (false);
	}
}
function isDigit(s) 
{ 
var patrn=/^[0-9]{1,20}$/; 
if (!patrn.exec(s)) return false 
return true 
} 
function rester(){
document.getElementById("dragonCode").value="";
document.getElementById("error").innerHTML="";

}