Firefox Extension - Multiple XMLHttpRequest calls per page

Question

I am trying to create a Firefox extension that can run multiple XMLHttpRequests per page. The code is below (my main function calls the makeRequest on different URLs). My proble

Answer 1

Your problem is you've only got one http_request identifier which is reused every time the makeRequest function is called. Here is one simple adjustment:-

function makeRequest(url,parameters) {
   var http_request = new XMLHttpRequest();
   if (http_request.overrideMimeType) {
      http_request.overrideMimeType('text/xml');
   }
   if (!http_request) {
      alert('Cannot create XMLHTTP instance');
      return false;
   }
   http_request.onreadystatechange = function() { 
           alertContents(http_request)
       };
   http_request.open('GET', url + parameters, true);
   http_request.send(null);
       return http_request;
}

function alertContents(http_request) {
   if (http_request.readyState == 4) {
      if (http_request.status == 200) {
            alert('Found: ' + http_request.responseText);
      } else {
         alert('There was a problem with the request.');
      }
              http_request.onreadystatechange = fnNull;
   }
}

    function fnNull() { };

The http_request identifier is local to each makeRequest execution. The correct instance of XHR is then passed to alerrContents each time onreadystatechange is fired by using a capture.

BTW, why separate url from parameters? Since the caller has to ensure the parameters argument is correctly url encoded it doesn't seem like a very useful abstraction. In addition the caller can simply pass a URL containing a querystring anyway.

Answer 2

this function can be further improved with cross browser functionality:

function makeRequest(method, url, parameters) {
    var http_request = false;
    if (window.XMLHttpRequest) { // Mozilla, Safari,...
        http_request = new XMLHttpRequest();
        if (http_request.overrideMimeType) {
            // set type accordingly to anticipated content type
            http_request.overrideMimeType('text/xml');
            //http_request.overrideMimeType('text/html');
        }
    } else if (window.ActiveXObject) { // IE
        try {
            http_request = new ActiveXObject("Msxml2.XMLHTTP");
        } catch (e) {
        try {
            http_request = new ActiveXObject("Microsoft.XMLHTTP");
        } catch (e) {}
        }
    }
    if (!http_request) {
        alert('Cannot create XMLHTTP instance');
        return false;
    }
    http_request.onreadystatechange = function() {
        alertContents(http_request);
    }
    url += (method=="GET")?parameters:"";
    http_request.open(method, url, true);
    if (method == "POST") {
        http_request.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
        http_request.setRequestHeader("Content-length", parameters.length);
        http_request.setRequestHeader("Connection", "close");
    }
    http_request.send((method=="GET")?null:parameters);
}