Uniqueness by id in Backbone.Collection

test.js

var _oldPrepareModel = Backbone.Collection.prototype._prepareModel;

Backbone.Collection.prototype._prepareModel = function (model, options) {
  var _id = model.id;
  if (!(model instanceof Backbone.Model)) _id = model[this.model.prototype.idAttribute];
  if (this._byId[_id]) return this.get(_id);
  return _oldPrepareModel.call(this, model, options);
}