ajax實現驗證數據庫里的用戶名和密碼

var xmlrequest;
function createXMLHttpRequest(){
 if(window.XMLHttpRequest){
 xmlrequest=new XMLHttpRequest();
 }
 else if(window.ActiveXObject){
 try{
 xmlrequest=new ActiveXObject("Msxm12.XMLHTTP");
 }
 catch(e){
 try{
 xmlrequest=new ActiveXObject("Microsoft.XMLHTTP");
 }
 catch(e){}
 }
 
 }
}
function login(){ 
 createXMLHttpRequest();
 var user = document.getElementById("yhm").value;
 var password = document.getElementById("mm").value;
 if(user==""||password==""){
 alert("請輸入用戶名和密碼!");
 return false;
 }
 var url = "check.php?user="+user+"&password="+password;
 xmlrequest.open("POST",url,true);
 xmlrequest.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
 xmlrequest.onreadystatechange = function(){
 if(xmlrequest.readyState == 4){
 if(xmlrequest.status==200){
 var msg = xmlrequest.responseText; 
 if(msg=='1'){
 alert('用戶名或密碼錯誤!');
 user="";
 password="";
 return false;
 } 
 else{ 
 window.location.href="index1.html";
 }
 }
 }
 }
 xmlrequest.send("user="+user+"&password="+password);
 }

<input placeholder="用戶名" autofocus="" type="text"name="username"> 
 <input placeholder="密碼" type="password" name="password">
 <button id="dl" onclick="login()">登錄</button>

<?php
$yhm1=$_POST['user'];
 $mm1=$_POST['password'];
@ $dp=new mysqli('localhost','root','你的密碼','你的數據庫名稱');
$yhm2=sha1($yhm1);
$mm2=sha1($mm1);
$query="select * from zhuce where yhm='$yhm2' and mm='$mm2'";
$result=$dp->query($query);
$num=$result->num_rows;
if(!$num){
 echo "1";
}
 
$dp->close();
 
?>