Store Backbone models in localStorage

It's time to use what you have learned about localStorage to store and retrieve objects. The DataStore object is responsible to transform models into strings to be stored in localStorage:

class DataStore {
  constructor(name) {
    this.name = name;

    // Keep track of all ids stored for a particular collection
this.index = this.getIndex();
  }

getIndex() {
var index = localStorage.getItem(this.name);
    return (index &&index.split(',')) || [];
  }
}

The DataStore object needs a name to be used as a collection index prefix. The first use case is to create a new item:

class DataStore {
// ...

  create(model) {
    // Assign an id to new models
    if (!model.id&& model.id !== 0) {
      model.id = generateId();
model.set(model.idAttribute, model.id);
    }

    // Save model in the store with an unique name,
    // e.g. collectionName-modelId
localStorage.setItem(
this.itemName(model.id), this.serialize(model)
    );

    // Keep track...