Backbone collection always with n models - backbone.js

Question

I'm trying make a list with last ten models or less on collection. I have events to add models dynamically with create. This event calls 'add' on collection and with my logic this add correctly one element. But I need add new element, check if collection has more than 10, if it's true remove last model and add new
var model = Backbone.Model.extend({
defaults: function() {
return {id:null}
}
});
var collection = Backbone.Collection.extend({
model:model
});
var view = Backbone.View.extend({
initialize: function(){
var self = this;
this.listenTo(collection, 'add', this.addOne);
this.listenTo(collection, 'reset', this.addAll);
this.listenTo(collection, 'all', this.render);
},
render: function(){
this.$el.html();
return this;
},
addAll: function(){
this.collection.each(this.addOne, this);
},
addOne: function(model){
//this is executed after 'create' but before this I need slice my collection
var view = new view({model:model});
this.$el.prepend(view.render().el);
}
});
thanks

Answer 1

Bind a function in initialize of your Backbone.Collection.extend on the add event in which you're checking the size.
initialize: function() {
this.on('add', function() {
this.checkSize();
});
},
checkSize: function() {
var max = 10;
if (this.length > max) {
this.reset(this.first(max));
}
}

Answer 2

Yoou can do like that:
addOne: function(model){
//this is executed after 'create' but before this I need slice my collection
if !model.get('new_field')
model.set({new_field, ""})
newField = new Date();
while (this.collection.findWhere({new_field:newField})){
newField = new Date();
}
model.set({new_field, newField});
var view = new view({model:model});
this.$el.prepend(view.render().el);
this.checkLength()
},
checkLength: function(){
if (this.collection.length > 10) {
// remove model which gets minimum value by 'new_field'
}
}