JqueryAjax+php实现简单的注册登录

HTML结构
<div class="container">
<form>
<label>用户名</label>
<input id="username" type="text" name="username" class="form-control" />
<label>密码</label>
<input id="password" type="password" name="password" class="form-control" />
<button type="button" id="login" class="btn btn-primary">登录</button>
<button type="button" id="sign" class="btn btn-danger">注册</button>
</form>
<div id="div"></div>
</div>前台JS$("#login").click(function(){
var sendData = {"username":$("#username").val(),"password":$("#password").val()}
$.ajax({
url:"action/login.php",
type:"POST",
data:sendData,
success:function(data){
if(data==1){
$("#div").html("密码正确")

}else if(data==2){
$("#div").html("密码不正确")
}else if(data==3){
$("#div").html("账号不存在")
}
}

})
})
$("#sign").click(function(){
var sendData = {"username":$("#username").val(),"password":$("#password").val()}
$.ajax({
url:"action/addUser.php",
type:"POST",
data:sendData,
success:function(data){
if(data==1){
$("#div").html("用户存在不能注册")
}else if(data==2){
$("#div").html("注册成功")
}
}

})
})后台login.php $username = $_POST['username'];
$password = $_POST['password'];
$conn = mysqli_connect("localhost","root","","login") or die("连接失败");
mysqli_query($conn,"set names utf8");
$result = mysqli_query($conn,"select * from user where username='$username'");

if($row=mysqli_fetch_array($result)){
if($row["password"]==$password){
echo 1;//密码正确
}else{
echo 2;//密码不正确
}
}else{
echo 3;//账号不正确
}后台addUser.php $username = $_POST['username'];
$password = $_POST['password'];
$conn = mysqli_connect("localhost","root","","login") or die("连接失败");
mysqli_query($conn,"set names utf8");
$result = mysqli_query($conn,"select * from user where username='$username'");
if($row=mysqli_fetch_array($result)){
echo 1;//"用户存在不能注册"
}else{
mysqli_query($conn,"insert into `user` (`username`,`password`) values ('$username','$password')");
echo 2;//注册成功
}
希望能对新手玩家有点帮助。