function loginCheck(){
	var userName = document.getElementById("userName"); 
	var userPassword= document.getElementById("userPassword");
	var error = "";
	if( userName.value == "" ) {
		error += "请输入用户名！\n";
	}
	else {
		if( !(/[0-9a-zA-Z-]{4,20}/).test( userName.value ) ) {
			error += "用户名格式错误：请输入4-20位字母、数字组合的用户名！\n"; 
		}
	}	
	if( userPassword.value == "" ) {
		error += "请输入密码！\n";
	}
	else {
		if( !(/[0-9a-zA-Z-]{4,20}/).test( userPassword.value ) ) {
			error += "密码格式错误: 请输入4-20位字母、数字组合的密码！\n";
		}
	}
	
	if( error != "" ) {
		alert(error);
		return false;
	}
}