Question

I’m trying to get my head around the Todo sample app for Backbone.js

While I have most of it understood there is one part I don’t get and was hoping someone could explain for me.

Looking at https://github.com/jeromegn/localtodos/blob/master/javascripts/todos.js

Line 162: How does the “todo” parameter in the function get here? I can’t see how it’s sent or from where?

Any help would be much appreciated and yes I will credit good answers now I know how it works on this site.

Thanks

Answer 1

In the AppView.initialize method, on line 146, the addOne method is registered as an event handler for the Todos collection’s add event.

Todos.bind('add', this.addOne);

When an item is added to the collection, Backbone triggers the add event, and passes the added model as the first argument to the event handler.

According to the list of built-in events, the add event handler method is passed the following arguments:

"add" (model, collection, options) — when a model is added to a collection.

That means that the addOne method could also receive two more arguments:

addOne: function(todo, todoscollection, options) {
    console.log(todo); // -> the model which was added
    console.log(todoscollection); // -> the collection, to which the model was added
    console.log(options); // -> the original options argument passed to collection.add
}

But because in Javascript declaring the full argument list is not necessary, the authors of the sample has chosen only to “receive” the first argument.