SOURCE CODE: Uize.Comm.Ajax (view docs)

/*______________
|       ______  |   U I Z E    J A V A S C R I P T    F R A M E W O R K
|     /      /  |   ---------------------------------------------------
|    /    O /   |    MODULE : Uize.Comm.Ajax Class
|   /    / /    |
|  /    / /  /| |    ONLINE : http://www.uize.com
| /____/ /__/_| | COPYRIGHT : (c)2004-2016 UIZE
|          /___ |   LICENSE : Available under MIT License or GNU General Public License
|_______________|             http://www.uize.com/license.html
*/

/* Module Meta Data
  type: Class
  importance: 9
  codeCompleteness: 95
  docCompleteness: 80
*/

/*?
  Introduction
    The =Uize.Comm.Ajax= class implements support for [[http://en.wikipedia.org/wiki/Ajax_(programming)][Ajax]] (Asynchronous JavaScript And XML) communication through the XMLHttpRequest (XHR) object.

    *DEVELOPERS:* `Jan Borgersen`, `Chris van Rensburg`, `Ben Ilegbodu`, `Tim Carter`, `Arthur Lee`, original code contributed by `Zazzle Inc.`

    In order to implement support for communication through the XMLHttpRequest object, this class overrides the implementation of the =performRequest= instance method inherited from the =Uize.Comm= base class. There are no additional methods or properties provided by this class - all the interface is provided in the =Uize.Comm= superclass.
*/

Uize.module ({
  name:'Uize.Comm.Ajax',
  required:'Uize.Url',
  builder:function (_superclass) {
    'use strict';

    /*** Class Constructor ***/
      var
        _nop = Uize.nop
      ;

    return _superclass.subclass ({
      instanceMethods:{
        performRequest:function (_request,_callback) {
          var
            m = this,
            _returnType = _request.returnType,
            _returnTypeIsObject = _returnType == 'object',
            _origUrl = Uize.Url.fromParams (_request.url),
            _requestUrl = Uize.Url.resolve (
              _request.url,
              Uize.copyInto (
                {
                  rnd:_request.cache == 'never' ? Uize.Url.getCacheDefeatStr () : null
                },
                _origUrl.comm_mode ? null : {comm_mode:'ajax'},
                _origUrl.output ? null : {output:'js'}
              )
            ),
            _requestData = _request.data || '',
            _requestMethod = _request.requestMethod,
            _requestMethodIsPost = _requestMethod == 'POST',
            _xmlHttpRequest = m._xmlHttpRequest || (
              m._xmlHttpRequest = window.XMLHttpRequest
                ? new XMLHttpRequest
                : new ActiveXObject ('Microsoft.XMLHTTP')
            )
          ;
          _xmlHttpRequest.onreadystatechange = function () {
            if (_xmlHttpRequest.readyState == 4) {
              _xmlHttpRequest.onreadystatechange = _nop;

              if (_xmlHttpRequest.status == 200) {
                var _responseText = _xmlHttpRequest.responseText;
                if (_returnTypeIsObject || _returnType == 'xml')
                  _request.responseXml = _xmlHttpRequest.responseXML
                ;
                if (_returnTypeIsObject || _returnType == 'text')
                  _request.responseText = _responseText
                ;
                if (_returnTypeIsObject || _returnType == 'json')
                  _request.responseJson = _responseText
                    ? Function ('var a=[' + _responseText + '];return a.pop()') ()
                    : null
                ;
                _xmlHttpRequest.abort();
                // no args means no error
                _callback ();
              }
              else {
                _xmlHttpRequest.abort();

                // callback with error object
                _callback ({
                  status: _xmlHttpRequest.status,
                  statusText: _xmlHttpRequest.statusText
                });
              }
            }
          };

          if (_xmlHttpRequest.upload) { // test if XHR2 upload support
            _xmlHttpRequest.upload.onprogress = function (_event) {
              m.fire({name: 'Progress', xhrEvent: _event});
            }
          }

          if (_requestMethodIsPost && !_requestData) {
            var _queryPos = _requestUrl.indexOf ('?');
            _requestData = _requestUrl.substr (_queryPos + 1);
            _requestUrl = _requestUrl.slice (0,_queryPos);
          }
          _xmlHttpRequest.open (_requestMethod,_requestUrl,true);
          if (_requestMethodIsPost) {
            // don't set the content-type request header if it's multipart/form-data; the built-in FormData object will take care of that
            _request.contentType != 'multipart/form-data' &&
              _xmlHttpRequest.setRequestHeader (
                'Content-type',
                _request.contentType || 'application/x-www-form-urlencoded'
              )
            ;
            //_xmlHttpRequest.setRequestHeader ('Content-length', _requestData.length);
          }
          _xmlHttpRequest.send (_requestData);
        }
      }
    });
  }
});