Two practices to extend Backbone model

bb-extend-bad.js

var Parent = Backbone.Model.extend({
      age : 3,
      ref: []
   });

var Child1 = Parent.extend(),
    Child2 = Parent.extend();

var c1 = new Child1(),
    c2 = new Child2();

c1.age = 10;
c1.ref.push(3);
c2.ref.push(4);

console.assert(c1.age !== c2.age, "age is not same");
console.assert(c1.ref !== c2.ref, "ref value is not name"); // Failure here !!!

bb-extend.good.js

var Parent = Backbone.Model.extend({
   defaults: function () {
      return {
         age : 3,
         ref: []
      };
   }});

var Child1 = Parent.extend({}),
    Child2 = Parent.extend({});

var c1 = new Child1(),
    c2 = new Child2();

c1.set('age', 10);

var xs = c1.get('ref');
xs.push(3);
c1.set('ref', xs);

var ys = c2.get('ref');
ys.push(4);
c2.set('ref', ys);

console.assert(c1.get('age') > 0);
console.assert(c2.get('age') > 0);
console.assert(c1.get('ref').length === 1);
console.assert(c2.get('ref').length === 1);

console.assert(c1.get('age') !== c2.get('age'), "age is not same");
console.assert(c1.get('ref') !== c2.get('ref'), "ref value is not name");

恩， 这个是个好方法。
另外在View等不支持defaults的地方， 我override 了他的constructor， 在里面this.ref = [];
var View = Backbone.View.extend( {

  cls : 'DefaultView',

  //use to generate unique id
  idMark : '__tz_id__',

  //whether to show default page
  enableDefaultPage : false,

  //Default Page of current View
  defaultPage : null,

  constructor : function(){
    /*default extend method usees swallow copy only, 
     * which mean that all instance share the same reference type, 
     * it causes chaos
     * */
    this.children = [];
    return Backbone.View.apply(this, arguments);
  },