请问大师们,查询注册用户名已存在时按钮不提交，不跳转，如何实现

请教大师们,查询注册用户名已存在时按钮不提交，不跳转，怎么实现？

PHP code

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请输入名称

JScript code

<!--Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/-->// JavaScript Documentvar XHR;function createXHR(){    if(window.ActiveXObject){        XHR=new ActiveXObject('Microsoft.XMLHTTP');    }else if(window.XMLHttpRequest){        XHR=new XMLHttpRequest();    }}function checkname(){    var username=document.form1.host.value;    createXHR();        XHR.open("GET","./checkname.php?id="+username,true);    XHR.onreadystatechange=byhongfei;    XHR.send(null);}function byhongfei(){    if(XHR.readyState == 4){        if(XHR.status == 200){                var textHTML=XHR.responseText;                        document.getElementById('msg').innerHTML=textHTML;        }    }}

PHP code

<!--Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/--><?php mysql_connect("localhost",'root','123456');    mysql_select_db('dodiscuz_freebb');    $sql="select * from member where username='$_GET[id]'";    $query=mysql_query($sql);    if(is_array(mysql_fetch_array($query))){        echo "用户名已存在";    }else{        echo "<font color=green>用户名可以使用";    }mysql_close();?>

用户名存在时 注册 按钮怎样实现不可用状态 现在就是用户名存在也跳转到index.php?reg

------解决方案--------------------

JScript code

document.getElementById("button").disabled    = 'true';//禁用document.getElementById("button").removeAttribute("disabled");//恢复<br><font color="#e78608">------解决方案--------------------</font><br>

JScript code

function byhongfei(){    if(XHR.readyState == 4){        if(XHR.status == 200){                var textHTML=XHR.responseText;                        document.getElementById('msg').innerHTML=textHTML;            if(textHTML == "用户名已存在"){              document.getElementById("button").disabled    = 'true';//禁用            }        }    }}<div class="clear">
                 
              
              
        
            </div>