JavaScript: promisified jQuery.ajax

jq-ajax-wrapper.js

// promisify $.ajax with Q
// =======================

var ns = {};

ns.ajax = (function($, Q){

  var defaults = {
      type: 'GET',
      async: true,
      // cache: false,
      crossDomain: true,
      contentType: 'application/json; charset=UTF-8'
    },
    callbacks = 'always,complete,done,error,fail,pipe,success'.split(','),
    length = callbacks.length;

  // enforce then-api
  // ----------------
  function hasRegisteredCallback(options){
    for(var i = length; i--;) if(callbacks[i] in options) return true;
    return false;
  }

  return function(options){

    if(hasRegisteredCallback(options)){
      throw new Error('use then-api instead of callbacks');
    }
    
    var deferred = Q.defer(),
        upload;

    // apply settings
    // --------------
    options = $.extend({}, defaults, options);

    // register progress handlers
    // --------------------------
    if(!('xhr' in options)){
      options.xhr = function(){
        var xhr = $.ajaxSettings.xhr(),
            $xhr = $(xhr);

        upload = xhr.upload;

        $xhr.on('readystatechange', function(evt){
          deferred.notify({evt: evt, msg: 'readystate', xhr: xhr});
        });

        if(upload){
          $xhr.on('progress', function(evt){
            deferred.notify({evt: evt, msg: 'upload', xhr: xhr});
          });
        }

        return xhr;
      };
    }

    // kick off
    // --------
    $.ajax(options)
      .done(function(data, msg, xhr) {
        deferred.resolve({data: data, msg: msg, xhr: xhr});
      })
      .fail(function(xhr, msg, err) {
        deferred.reject({error: err, msg: msg, xhr: xhr});
      })
      .always(function(xhr){
        if(upload) $(upload).off('progress');
        $(xhr).off('readystatechange');
      });
    
    return deferred.promise;
  };
}(jQuery, Q));