javascript - 检查innerHTML是否为空

Question

我对 onkeyup 事件进行了 ajax 调用，该调用检查给定的电子邮件地址是否在数据库中。我的问题是，我找不到正确的解决方案来检查 ajax 响应是否为空，如果是，我需要禁用按钮。

这是 ajax.php 输出:

$sql = "// the query";

$result = mysql_query($sql);
$num_rows = mysql_num_rows($result);

if($num_rows>0){
    echo "<i>Yepp, this is taken</i>";
  }

这是用于 ajax 调用和按钮禁用和启用功能的 JavaScript(仅当电子邮件地址有效时才调用 ajax):

function checkEmail(str){

    email = document.getElementById('user-email').value
    AtPos = email.indexOf("@")
    StopPos = email.lastIndexOf(".")

    if (AtPos == -1 || StopPos == -1) {
         document.getElementById('button-reg').disabled=true;    
    }else{
        if (str=="")
          {
          document.getElementById("txtHint").innerHTML="";
          return;
          }
        if (window.XMLHttpRequest)
          {// code for IE7+, Firefox, Chrome, Opera, Safari
          xmlhttp=new XMLHttpRequest();
          }
        else
          {// code for IE6, IE5
          xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
          }
        xmlhttp.onreadystatechange=function()
          {
          if (xmlhttp.readyState==4 && xmlhttp.status == 200){
                document.getElementById("txtHint").innerHTML=xmlhttp.responseText;
            }
          }
        xmlhttp.open("GET","ajax.php?q="+str,true);
        xmlhttp.send();
    }
    var htmlstring = document.getElementById("txtHint").innerHTML;

    htmlstring = htmlstring.replace(/^\s+/,'');
    
    if(htmlstring==""){
        document.getElementById('button-reg').disabled=false;
    }else{
        document.getElementById('button-reg').disabled=true;
    }
}

正如你所看到的，我尝试消除空格，但没有运气...空响应后按钮仍然没有禁用...

有人可以帮我吗？

Answer 1

使用此功能..

function checkEmail(str){

    email = document.getElementById('user-email').value
    AtPos = email.indexOf("@")
    StopPos = email.lastIndexOf(".")

    if (AtPos == -1 || StopPos == -1) {
         document.getElementById('button-reg').disabled=true;    
    }else{
        if (str=="")
          {
          document.getElementById("txtHint").innerHTML="";
          return;
          }
        if (window.XMLHttpRequest)
          {// code for IE7+, Firefox, Chrome, Opera, Safari
          xmlhttp=new XMLHttpRequest();
          }
        else
          {// code for IE6, IE5
          xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
          }
        xmlhttp.onreadystatechange=function()
          {
          if (xmlhttp.readyState==4 && xmlhttp.status == 200){
                document.getElementById("txtHint").innerHTML=xmlhttp.responseText;

                htmlstring = xmlhttp.responseText.replace(/^\s+/,'');
                if(htmlstring==""){
                    document.getElementById('button-reg').disabled=false;
                }else{
                    document.getElementById('button-reg').disabled=true;
                }
            }
          }
        xmlhttp.open("GET","ajax.php?q="+str,true);
        xmlhttp.send();
    }
}

希望这有帮助..