案例：简单验证用户名是否存在(post请求)

案例需求：

  我们这里用php数组模拟一个数据库，然后运用onblur事件通过Ajax实现用户名验证是否可以。

• js代码

    <script>
    window.onload = function(){
        var username = document.getElementById('username');
        var pwd = document.getElementById('password');
        username.onblur = function(){
            var userValue = username.value;
  
            //1.创建XMLHttpRequest对象
            var xhr = null;
            if( window.XMLHttpRequest ){
                xhr = new XMLHttpRequest();  //常规浏览器
            }else{
                xhr = new ActiveXObject( "Microsoft.XMLHTTP" );   //IE6
            }
  
            //2.准备发送
            var str = 'username =' + userValue;
            xhr.open( 'post','demo-post.php',true );
  
            //3.执行发送动作
            //post请求必须设置请求头 setRequestHeader
            xhr.setRequestHeader('Content-Type','application/x-www-form-urlencoded');
            xhr.send(str);    //post请求时这里是传送到服务器端的字符串
  
            //4.指定回调函数
            xhr.onreadystatechange = function(){
                if( xhr.readyState == 4 && xhr.status == 200 ){
                    var data = xhr.responseText;
                    var info = document.getElementById('info');
                    if( data == '1' ){
                        info.innerHTML='用户可用';
                        info.style.color='yellowgreen';
                    }else if( data == '2' ){
                        info.innerHTML = '用户名以存在';
                        info.style.color = 'red';
                    }
                }
            };
        };
    };
    </script>
  

• html代码

    <form>
        用户：<input type="text" name="username" id="username"><span id="info"></span><br>
        密码：<input type="password" name="password" id="password">
    </form>

• php代码

    <?php
        $arry = array('super','kobe','admin');
        $username = $_POST['username'];
        $flag = false;
        foreach ( $arry as $value ) {
            if( $username == $value ){
                $flag = true;
                break;
            }
        }
        if( $flag == true ){
            echo "2";
        }else if( $flag == false ) {
            echo "1";
        }
    ?>