Override fetch method in backbone

Question

i want to override the fetch method in models as well as in collections for fetching the data from localstorage when there is no network connection.

This is a fetch function inside a collection

fetch:function(){
   if(online){
      return Backbone.Collection.prototype.fetch.call(this) ;
   }else{
    // return Backbone.Collection.fetch event - with data from localstorage 
   }
}

i am facing 2 problems here

a.The success nor error function are not been executed

this.collection.fetch({
   success: function(data){ ... },
   error: function(){ ... }
});

b. If there is no connection how do set the data to the collection so that i can access it in success function

Answer 1

Try something like this. $.ajax returns a promise so you should be able to do the following

fetch:function(){
   var dfd = new jQuery.Deferred();
   if(this.online){
      return Backbone.Collection.prototype.fetch.call(this) ;
   }else{
     // Do your logic for localstorage here
     dfd.resolve();
   }

   return dfd.promise();
}

Then you can use your above example or as I prefer

this.collection.fetch().then(function() { 
    console.log('Successfully fetched from localstorage or server.'); 
});

Answer 2

After researching i have found the answer for problem a.

fetch:function(options){
    if(navigator.onLine){
        return Backbone.Collection.prototype.fetch.apply(this, options) ;
    }else{
     return //Trying to findout
    }
}

After passing option argument to fetch function and arguments to fetch.apply we will be able to access the success function from the calling function