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javascriptbackbone.js

Missing argument in callback function for localTodos app

Here is the source - Todo Javascript Source

addOne expects one argument

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

as you can see here:

addOne: function(todo) {
  var view = new TodoView({model: todo});
  this.$("#todo-list").append(view.render().el);
},

where does it get this, the callback appears to call the function with no arguments?

Solution

  • This line

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

    tells you precisely nothing about how many arguments will be provided to the callback.

    In fact, Backbone event callbacks receive varying numbers of params which are all cataloged here: http://backbonejs.org/#Events-catalog

    In the specific case of add, the callback params are model, collection, and options.