Load JSON file into model using Javascript / jQuery (deferred, asynchronous)

Question

As a beginner I am always determined to improve myself. I've got written the following Code using jQuery that is working fine. However, I am sure that there are cleaner ways for achieving the same.

Right now, I am struggling with the this keyword and the asynchronous loading of the JSON file. Moreover, I am not sure whether you should call an function for initialization the way I did.

Do you have any suggestions for improvements?

$(function(){

    function Model() {
        this.data = null;
        this.init();
    };

    Model.prototype = {

        deferred: $.Deferred(),

        config: {
            jsonFile: 'dump.json'
        },

        init: function() {
            this.loadJson();
        },

        loadJson: function() {
            var self = this;
            jQuery.getJSON(
                this.config.jsonFile,
                function(data) {
                    self.data = data;
                    self.deferred.resolve();
                }
            )
            .fail(function() {
                console.error("Loading JSON file failed");
            })
            .always(function() {});
        },

        getData: function(callback) {
            console.log("getData")
            var self = this;

            $.when(this.deferred)
            .done(function() {
                callback(self.data)
            })
        },
    };

    var model = new Model();
    model.getData(function(data) {
        console.log(data)
    });

});

(duplicate of https://stackoverflow.com/q/23142089/3546614)

Update 1

I've just updated my code (and truncated unimportant stuff) taking @jgillich's advices into account. For the moment I feel better reading the JSON file when the object is generated which is why I outsourced the operation into separate function.

$(function(){
    function Model() {
        this.loadJson();
    };

    Model.prototype = {

        deferred: $.Deferred(),
        jsonFile: 'dump.json',

        loadJson: function() {
            $.getJSON(this.jsonFile)
                .done(function (data) {
                    this.data = data;
                    this.deferred.resolve(data);
                }.bind(this))
                .fail(this.deferred.reject);
        },

        getData: function() {
            return this.deferred.promise();
        },
    };

    var model = new Model();
    model.getData().done(function(data) {
        console.log('done')
        console.log(data)
    });
});

Answer 1

• Storing deferred in the model and then passing a callback to getData is a bit obscure. You could write it like this instead:

  getData: function() {
      var deferred = $.Deferred();
  
      if(!this.data) {
          $.getJSON('...',).done(function (data) {
              this.data = data;
              deferred.resolve(data);
          }.bind(this)).fail(deferred.reject);
      } else {
          deferred.resolve(this.data);
      }
  
      return deferred.promise();
  }
  
  model.getData().done(function (data) { /* ... */});
  

• Use either $ or jQuery, don't mix them.

• Use Function.prototype.bind instead of var self = this.

• Use semicolons after each statement (or leave them out entirely if you prefer that).

• this.data = null; seems pointless, newly created objects don't have such a property.