fabric.js/src/util/dom_request.js

(function(){
  
  function addParamToUrl(url, param) {
    return url + (/\?/.test(url) ? '&' : '?') + param;
  }
  
  var makeXHR = (function() {
    var factories = [
      function() { return new ActiveXObject("Microsoft.XMLHTTP"); },
      function() { return new ActiveXObject("Msxml2.XMLHTTP"); },
      function() { return new ActiveXObject("Msxml2.XMLHTTP.3.0"); },
      function() { return new XMLHttpRequest(); }
    ];
    for (var i = factories.length; i--; ) {
      try {
        var req = factories[i]();
        if (req) {
          return factories[i];
        }
      }
      catch (err) { }
    }
  })();

  function emptyFn() { };

  function request(url, options) {

    options || (options = { });

    var method = options.method ? options.method.toUpperCase() : 'GET',
        onComplete = options.onComplete || function() { },
        request = makeXHR(),
        body;
        
    /** @ignore */
    request.onreadystatechange = function() {
      if (request.readyState === 4) {
        onComplete(request);
        request.onreadystatechange = emptyFn;
      }
    };
    
    if (method === 'GET') {
      body = null;
      if (typeof options.parameters == 'string') {
        url = addParamToUrl(url, options.parameters);
      }
    }

    request.open(method, url, true);
    
    if (method === 'POST' || method === 'PUT') {
      request.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
    }

    request.send(body);
    return request;
  };
  
  fabric.util.request = request;
})();