var xmlHttp;
var returnMark = 3;

function createXMLHttpRequest() {
    if(window.XMLHttpRequest) { 
    //alert('creating');
        xmlHttp = new XMLHttpRequest();
    } else if (window.ActiveXObject) { 
        try {
            xmlHttp = new ActiveXObject("Msxml2.XMLHTTP");
        } catch (e) {
	        try {
	             xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
	        } catch (e) {
	        }
        }
    }
}
function handleStateChange() {
    if (xmlHttp.readyState == 4) {
        if (xmlHttp.status == 200) {
            updateList();
        }
    }
         //alert(xmlHttp.status);
}
function updateList(){
	var returnText = xmlHttp.responseText;
	//alert(returnText);
	if(document.form1.user_name.value.length > 22 || document.form1.user_name.value.length < 5){
			document.getElementById("checkMsg").innerHTML = "<font color='red'>用户名在5-22个字符之间,请重新输入</font>&nbsp;&nbsp;&nbsp;&nbsp;";	
			return;
	}
	if(returnText == -1){
		returnMark = -1;
		document.getElementById("checkMsg").innerHTML = "<font color='red'>用户名含有特殊字符,请重新输入</font>&nbsp;&nbsp;&nbsp;&nbsp;";	

	}else if(returnText == 0){
		returnMark = 2;
		document.getElementById("checkMsg").innerHTML = "<font color='red'>此账号已存在</font>&nbsp;&nbsp;&nbsp;&nbsp;";	

	}else if(returnText == 1){
		document.getElementById("checkMsg").innerHTML = "<font color='green'>可以使用</font>&nbsp;&nbsp;&nbsp;&nbsp;";
		returnMark = 1;				
	}else{
		document.getElementById("checkMsg").innerHTML = "<font color='green'>验证时系统发生错误，请重新验证</font>&nbsp;&nbsp;&nbsp;&nbsp;";
		returnMark = 3;					
	}
}

function check(){
	if(document.getElementById('user_name').value == ''){
		alert('请填写用户名');	
		return false;
	}
    createXMLHttpRequest();	
	var URL ="user.php?act=isuserexist&username="+encodeURI(document.getElementById('user_name').value);
	//alert(URL);
	xmlHttp.onreadystatechange=handleStateChange;
	xmlHttp.open("GET", URL,true);
	xmlHttp.send(null);	
	document.getElementById("checkMsg").innerHTML = "正在检查账号，请等候.....&nbsp;&nbsp;&nbsp;&nbsp;";
	/**/
}