<div id="reg">
  <label>用户名:<input type="text" id="username" /></label><label></label><br /><br />
  <label>密码:<input type="password" id="passw" /></label><br /><br />
  <label>确认密码:<input type="password" id="repassw" /></label><br /><br />
  <label>邮箱:<input type="text" id="email" /></label><br /><br />
  <button id="btn">注册</button>
  <span id="user"></span>
  <span id="pass"></span>
  <span id="rep"></span>
  <span id="em"></span>
 </div>

#reg{width:400px;height: 300px;position: relative;margin:10px auto}
  #reg label{float:right;position: relative;margin-top: 10px;font-size: 28px;}
  #reg label input{width:250px;height: 40px;font-size: 24px;}
  #reg #btn{width:120px;height: 40px;position: absolute;right: 65px;margin-top: 80px;}
  #reg span{width:200px;position: absolute;right: -210px;font-size: 24px;}
  #reg #user{top:20px;}
  #reg #pass{top:75px;}
  #reg #rep{top:130px;}
  #reg #em{top:185px;}
  .error{color:red;}
  .ok{color:greenyellow;}

 <script src="../../../ajax.js"></script>
 <script>
  window.onload = function ()
  {
   //后台验证
   bgProcess();
   //提交注册信息，返回注册成功与否
   $('btn').onclick = function ()
   {
    var jsonData = {username:$('username').value,passw:$('passw').value,
     repassw:$('repassw').value,email:$('email').value};
    ajax('regProccess.php',jsonData,getInfo,'json');
   };
   function getInfo(info)
   {
    var a = ['username','passw','repassw','email'];
    var b = ['user','pass','rep','em'];
    var flag = true;
    for(var i =0;i<info.length;i++)
    {
     if(info[i].state == 'false')
     {
      flag = false;
      displayInfo(info[i],b[i],a[i]); //显示错误信息
     }
    }
    if(flag) alert('恭喜你注册成功');
   }
  };
  //后台验证
  function bgProcess()
  {
   //验证用户名
   $('username').onblur = function ()
   {
    var jsonData = {username:this.value};
    ajax('regProccess.php',jsonData,getUser,'json');
   };
   function getUser(msg)
   {
    displayInfo(msg[0],'user','username');
   }
   //验证密码
   $('passw').onkeyup = $('passw').onblur= function ()
   {
    var jsonData = {passw:this.value};
    ajax('regProccess.php',jsonData,getPass,'json');
   };
   function getPass(msg)
   {
    displayInfo(msg[1],'pass','passw');
   }
   //确认密码
   $('repassw').onblur = function ()
   {
    var jsonData = {passw:$('passw').value,repassw:this.value};
    ajax('regProccess.php',jsonData,getRepass,'json');
   };
   function getRepass(msg)
   {
    displayInfo(msg[2],'rep','repassw');
   }
   //验证邮箱
   $('email').onblur= function ()
   {
    var jsonData = {email:this.value};
    ajax('regProccess.php',jsonData,getEmail,'json');
   };
   function getEmail(msg)
   {
    displayInfo(msg[3],'em','email');
   }
  }
  //显示信息
  function displayInfo(msg,id,name)
  {
   $(id).className = (msg.state == 'true')?'ok':'error';
   $(id).innerHTML = msg[name];
  }
  function $(id)
  {
   return document.getElementById(id);
  }
 </script>

<?php
/**
 * @function 验证用户名
 * @param $username 用户名
 * @return 返回一个$res数组，里面包含了错误代码,1:用户名非法，1：没有输入用户名，1：用户名存在
 */
function verifyUser($username)
{
 $res = array();
 //匹配成功返回匹配次数，0表示没有匹配到,匹配字母、数字、下划线
 if(preg_match("/^\\w{6,16}$/",$username) == 0)
  $res[] = 1;
 else
  $res[] = 0;
 if(empty($username))
  $res[] = 1;
 else
  $res[] = 0;
 if(verifyData($username,'用户名')) //验证该用户名是否被注册了
  $res[] = 1;
 else
  $res[] = 0;
 return $res;
}

/**
 * @function 验证密码是否非法和密码强度
 * @param $passw 密码
 * @return $res 密码强度
 */
function verifyPassw($passw)
{

 $reg1 = '/^[0-9]{8,16}$/'; //纯数字
 $reg2 = '/^[a-zA-Z]{8,16}$/';//纯字母
 $reg3 = '/^[a-zA-Z\+]{8,16}$/';//纯字母+
 $reg4 = '/^[0-9a-zA-Z]{8,16}$/';//数字和字母组合
 $reg5 = '/^[0-9a-zA-Z\+]{8,16}$/';//数字、'+‘和字母组合
 $res;
 if(empty($passw))
  $res = -1;
 else if(preg_match($reg1,$passw))
  $res = 1;
 else if(preg_match($reg2,$passw))
  $res = 1;
 else if(preg_match($reg3,$passw))
  $res = 2;
 else if(preg_match($reg4,$passw))
  $res = 2;
 else if(preg_match($reg5,$passw))
  $res = 3;
 else
  $res = 0; //非法密码
 return $res;
}

/**
 * @function 验证邮箱是否非法和是否已经被注册使用
 * @param $email 邮箱
 * @return $res 错误代码
 */
function verifyEmail($email)
{

 $reg = '/^([\w-*\.*])+@(\w-?)+(\.\w{2,})+$/';
 $res;
 if(empty($email))
  $res = -1;
 else if(verifyData($email,'邮箱'))
  $res = 1;
 else if(preg_match($reg,$email))
  $res = 2;
 else
  $res = 0; //非法邮箱
 return $res;
}

/**
 * @function 验证data是否已经存在
 * @param $data
 * @param $query
 * @return data存在返回1，否则返回0
 */
function verifyData($data,$query)
{
 //1.连接数据库
 @$db = new MySQLi('localhost','root','root','user_passd');
 if(mysqli_connect_errno())
  die("连接数据库失败");
 //2.验证数据是否存在
 $sql = "select $query from login where $query = '{$data}'";
 $res = $db->query($sql);
 $row = $res->fetch_assoc();
 //3.关闭数据库
 $db->close();
 return is_null($row)?0:1;
}

/**
 * @function 保存注册用户信息
 * @param $data 要保存的数据，一个数组
 * @return bool $res 返回true表示信息保存成功，false表示失败
 */
function saveRegInfo($data)
{
 //1.连接数据库
 @$db = new MySQLi('localhost','root','root','user_passd');
 if(mysqli_connect_errno())
  die("连接数据库失败");
 //2.插入数据
 $sql = "insert into login values('{$data[0]}','{$data[1]}','{$data[2]}')";
 $res = $db->query($sql);
 //3.关闭数据库
 $db->close();
 return $res;
}

<?php

header("Content-Type:text/html;charset=utf-8");
//禁用缓存,是为了数据一样的前提下还能正常提交，而不是缓存数据
header("Cache-Control:no-cache");
include('myFunc.php'); //包含我的函数库
$username = isset($_POST['username'])?$_POST['username']:''; //获取用户名
$passw =isset($_POST['passw'])?urlencode($_POST['passw']):'';  //获取密码
$repassw = isset($_POST['repassw'])?urlencode($_POST['repassw']):''; //获取确认密码
$email = isset($_POST['email'])?$_POST['email']:''; //获取邮箱
$info='[';   //存放返回页面的数据
$isSucceed = 0; //判断注册是否成功,如果最后结果为4，则意味着全部正确，注册成功
//1.验证用户名是否非法
$res1 = verifyUser($username);
if($res1[1])
 $info.='{"username":"请输入用户名","state":"false"}';
else if($res1[0])
 $info.='{"username":"用户名非法","state":"false"}';
else if($res1[2])
 $info.='{"username":"用户名已存在","state":"false"}';
else
{
 $info.='{"username":"用户名可用","state":"true"}';
 ++$isSucceed;
}
$info.=',';
//2.验证密码是否非法和强度
$res2 = verifyPassw($passw);
if($res2 == -1)
 $info.='{"passw":"请输入密码","state":"false"}';
else if($res2 == 0)
 $info.='{"passw":"密码非法","state":"false"}';
else
{
 if($res2 == 1)
 $info.='{"passw":"密码强度较弱","state":"true"}';
 else if($res2 == 2)
 $info.='{"passw":"密码强度中等","state":"true"}';
 else if($res2 == 3)
 $info.='{"passw":"密码强度较强","state":"true"}';
 ++$isSucceed;
}

$info.=',';

//3.确认密码
if(empty($repassw))
 $info.='{"repassw":"请先输入密码","state":"false"}';
else if($passw == $repassw)
{
 $info.='{"repassw":"密码一致","state":"true"}';
 ++$isSucceed;
}
else
 $info.='{"repassw":"密码不一致","state":"false"}';
$info.=',';

//4.验证邮箱
$res3 = verifyEmail($email);
if($res3 == -1)
 $info.='{"email":"请输入邮箱","state":"false"}';
else if($res3 == 0)
 $info.='{"email":"邮箱非法","state":"false"}';
else if($res3 == 1)
 $info.='{"email":"此邮箱已被注册","state":"false"}';
else if($res3 == 2)
{
 $info.='{"email":"此邮箱可用","state":"true"}';
 ++$isSucceed;
}
//保存用户注册信息
if($isSucceed == 4)
 saveRegInfo(array($username,$passw,$email));
echo $info.=']';