Backbone.js: _.bindAll() in initialize - why is this used?

I've been looking at some examples of backbone.js based application. I notice that in some (such as this example below) the underscore function _.bindAll() is used:

 initialize: function (a开发者_如何学编程rgs) {
        _.bindAll(this, 'changeTitle');
        this.model.bind('change:title', this.changeTitle);
    },

whereas in others (such as the todo app below) do not:

initialize: function() {
  this.model.bind('change', this.render, this);
  this.model.bind('destroy', this.remove, this);
},

What is the purpose of _.bindAll() in this context, and is it necessary?

_.bindAll() changes this in the named functions to always point to that object, so that you can use this.model.bind(). Notice that in your second example, a third argument is passed to bind(); that's why using _.bindAll() isn't necessary in that case. In general, it's a good idea to use for any methods on the model that will be used as callbacks to events so that you can refer to this more easily.

In Detail: _.bind(ctx, 'method')

Takes your method, creates a copy with the context bound to 'ctx' and adds the copy as property.

This is a workaround for jQuery.bind() not allowing you to pass in a context. JQ will always call the callbacks with a undefined context. Backbone is built on jQuery.

See here: http://backbonejs.org/#FAQ-this