Browser compatibility with AJAX function

I have the following AJAX function that calls a PHP file to determine if an email is present in a db.

<script language="javascript" type="text/javascript">
//Browser Support Code
function ajaxFunction(Email){

    var url="index.php?EmailCheck=Yes&Email=" + Email;

var ajaxRequest;  // The variable that makes Ajax possible!

try{
    // Opera 8.0+, Firefox, Safari
    ajaxRequest = new XMLHttpRequest();
} catch (e){
    // Internet Explorer Browsers
    try{
        ajaxRequest = new ActiveXObject("Msxml2.XMLHTTP");
    } catch (e)开发者_如何学C {
        try{
            ajaxRequest = new ActiveXObject("Microsoft.XMLHTTP");
        } catch (e){
            // Something went wrong
            alert("Your browser broke!");
            return false;
        }
    }
}
// Create a function that will receive data sent from the server
ajaxRequest.onreadystatechange = function(){
    if(ajaxRequest.readyState == 4){
        if(ajaxRequest.responseText == 0) {
                    alert("Sorry that email is not registered.");
                    } else {
                    alert("Login successful.");
                    window.opener.location.reload();
                    window.close();
                    }
    }
}

ajaxRequest.open("GET", url, true);
ajaxRequest.send(null); 

}

Are there going to be any browsers this won't work for? I have had some complaints from users, but I can't replicate the errors in IE, FF, or Chrome.

It won't work in Lynx, and it probably won't work in some specialized screen-reader browsers. If you seriously expect to have users for which it won't work, for God's sake fix the error message. Better yet, use something like jQuery. Realize that it's possible to fall back to an alternative approach of using a hidden <iframe> or something instead of XMLHTTPRequest.