collection_add.js

function Model(name) {
  this.name = name;
}

function Collection(models) {
  this.models = models || [];
}
Collection.prototype.showName = function() {
  this.models.forEach(function(model) {
    console.log(model.name);
  });
}
Collection.prototype.add = function(model) {
  this.models.push(model);
}

var model1 = new Model("hoge1");
var model2 = new Model("hoge2");
var model3 = new Model("hoge3");
var model4 = new Model("hoge4");

var collection1 = new Collection();
var collection2 = new Collection();

collection1.add(model1);
collection1.add(model3);

collection2.add(model2);
collection2.add(model4);

collection1.showName();
collection2.showName();