javascript！=不起作用

i have a script that i have written. But the not equal to operator is not working correctly

 if((ajax.responseText) != "success"){
                    alert("nice oneagain");
                    alert(ajax.responseText);
                    _(submiit).style.display = "block";
                    _(status).innerHTML = '';
                } else {
                    alert("Complaint escalated");
                    _(status).innerHTML = 'Complaint escalated';
                }

here even though the server returns ajax.responseText = success then also it never goes in the else. and only the if part is executed evry time.

if((ajax.responseText.toString().trim()) != "success"){
                    alert("nice oneagain");
                    alert(ajax.responseText);
                    _(submiit).style.display = "block";
                    _(status).innerHTML = '';
                } else {
                    alert("Complaint escalated");
                    _(status).innerHTML = 'Complaint escalated';
                }

//instead of checking for responseText check for readystate and status
<script>
if(ajax.readyState==4 && ajax.status ==200){
    alert("nice oneagain");
    alert(ajax.responseText);
    _(submiit).style.display = "block";
    _(status).innerHTML = '';
} else {
    alert("Complaint escalated");
    _(status).innerHTML = 'Complaint escalated';
}
 <script>