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() { }

  /**
   * Cross-browser abstraction for sending XMLHttpRequest
   * @memberOf fabric.util
   * @param {String} url URL to send XMLHttpRequest to
   * @param {Object} [options] Options object
   * @param {String} [options.method="GET"]
   * @param {Function} options.onComplete Callback to invoke when request is completed
   * @return {XMLHttpRequest} request
   */
  function request(url, options) {

    options || (options = { });

    var method = options.method ? options.method.toUpperCase() : 'GET',
        onComplete = options.onComplete || function() { },
        xhr = makeXHR(),
        body;

    /** @ignore */
    xhr.onreadystatechange = function() {
      if (xhr.readyState === 4) {
        onComplete(xhr);
        xhr.onreadystatechange = emptyFn;
      }
    };

    if (method === 'GET') {
      body = null;
      if (typeof options.parameters === 'string') {
        url = addParamToUrl(url, options.parameters);
      }
    }

    xhr.open(method, url, true);

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

    xhr.send(body);
    return xhr;
  }

  fabric.util.request = request;
})();