JS——我的第三个AJAX程序（带数据库的用户名输入验证，模仿注册）

前端：

common.js

function $(id) {
	return document.getElementById(id);
}

function createXhr(){
	var xhr;
	if(window.XMLHttpRequest){
		xhr = new XMLHttpRequest();
	}else{
		xhr = new ActiveXObject("Microsoft XMLHttp");
	}
	return xhr;
}

checkuname.html

<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Document</title>
	<script src="common.js"></script>
</head>
<body>
	用户名：
	<input type="text" id="uname" onblur="getMsg()">
	<span id="unameTip"></span>
	<script>
		function getMsg() {
			var uname = $("uname").value;
			if(uname == null || uname == ""){  //这里可以优化，用JS的正则来处理多个空格以及禁止的特殊字符
				$("unameTip").innerHTML = "用户名不能为空";
				return;
			}
			//console.log("333");
			var xhr = createXhr();
			xhr.open("GET","checkuname.php?uname="+uname,true);
			xhr.onreadystatechange = function() {
				if(xhr.readyState == 4 && xhr.status == 200){
					var resText = xhr.responseText;
					if(resText == 0){
						$("unameTip").innerHTML = "用户名可以使用";
					}else if(resText == 1){
						$("unameTip").innerHTML = "用户名已存在，请更换";
					}else{
						$("unameTip").innerHTML = "异常，请刷新页面";
					}
				}
			}
			xhr.send(); //这个别忘了
		}
	</script>
</body>
</html>

后台：

init.php

<?php 

	$conn = mysqli_connect('127.0.0.1','root','','xz',3306);
	$initsql = "SET NAMES UTF8";
	mysqli_query($conn,$initsql);
?>

checkuname.php

<?php 

	@$uname = $_REQUEST["uname"];
	if($uname == null || $uname == ""){
		die("uname required");
	}

	require("init.php");

	$sql = "SELECT * FROM xz_user WHERE uname = '$uname'"; //别忘了WHERE
	$result = mysqli_query($conn,$sql);
	
	if($result === false){
		// echo "执行失败，请检查sql语句<br>";
		// echo $sql;
		echo null;
	}else{
		$count = mysqli_affected_rows($conn);
		//echo $count . "<br>";
		if($count == 0){
			echo 0;
		}else{
			echo 1;
		}
	}
?>