下划线_.each和forEach有什么区别？

Question

I study Backbone n underscore.
somebody help me.
I don't know that model is undefined of _.each().

 var todos = new Backbone.Collection();

    todos.add([
        { title: 'go to Belgium.', completed: false },
        { title: 'go to China.', completed: false },
        { title: 'go to Austria.', completed: true }
    ]);

    // iterate over models in the collection 
    todos.forEach(function(model){
        console.log(model.get('title'));
    });
    // Above logs:
    // go to Belgium.
    // go to China.
    // go to Austria.

Why model is undefined???

    /*underscoreJS  model is undefined...*/
    _.each(todos, function (model) {
        console.log(model.get('title'));
    });

Answer 1

For underscore you need to do like this:

 _.each(todos.models, function(model) {
   console.log(model.get('title'));
 });

Reason when you do

 var todos = new Backbone.Collection();

 todos.add([{
   title: 'go to Belgium.',
   completed: false
 }, {
   title: 'go to China.',
   completed: false
 }, {
   title: 'go to Austria.',
   completed: true
 }]);

Backbone returns a proxy object which hold the model array in todos.models

working code here