Example ES6 file

gistfile1.js

import _ from 'lodash';

let records = Symbol('records'),
  find = Symbol('find');

class TallyItemModel {
  constructor() {
    this[records] = [];
  }

  add(itemName) {
    this[records].push({
      count: 0,
      item: itemName
    });
  }

  decrement(itemName) {
    let item = this[find](itemName);

    item.count--;
  }

  getAllRecords() {
    return _.clone(this[records]);
  }

  increment(itemName) {
    let item = this[find](itemName);

    item.count++;
  }

  [find](itemCount) {
    return _.find(this[records], { item: itemName });
  }
}

export default TallyItemModel;