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backbone-localstorage.js todos.js

# backbone-localstorage.js

¶

A simple module to replace `Backbone.sync` with localStorage-based persistence. Models are given GUIDS, and saved into a JSON object. Simple as that.

¶

Generate four random hex digits.

    function S4() {
       return (((1+Math.random())*0x10000)|0).toString(16).substring(1);
    };

¶

Generate a pseudo-GUID by concatenating random hexadecimal.

    function guid() {
       return (S4()+S4()+"-"+S4()+"-"+S4()+"-"+S4()+"-"+S4()+S4()+S4());
    };

¶

Our Store is represented by a single JS object in localStorage. Create it with a meaningful name, like the name you'd give a table.

    var Store = function(name) {
      this.name = name;
      var store = localStorage.getItem(this.name);
      this.data = (store && JSON.parse(store)) || {};
    };

    _.extend(Store.prototype, {

¶

Save the current state of the Store to localStorage.

      save: function() {
        localStorage.setItem(this.name, JSON.stringify(this.data));
      },

¶

Add a model, giving it a (hopefully)-unique GUID, if it doesn't already have an id of it's own.

      create: function(model) {
        if (!model.id) model.id = model.attributes.id = guid();
        this.data[model.id] = model;
        this.save();
        return model;
      },

¶

Update a model by replacing its copy in `this.data`.

      update: function(model) {
        this.data[model.id] = model;
        this.save();
        return model;
      },

¶

Retrieve a model from `this.data` by id.

      find: function(model) {
        return this.data[model.id];
      },

¶

Return the array of all models currently in storage.

      findAll: function() {
        return _.values(this.data);
      },

¶

Delete a model from `this.data`, returning it.

      destroy: function(model) {
        delete this.data[model.id];
        this.save();
        return model;
      }

    });

¶

Override `Backbone.sync` to use delegate to the model or collection's localStorage property, which should be an instance of `Store`.

    Backbone.sync = function(method, model, success, error) {

      var resp;
      var store = model.localStorage || model.collection.localStorage;

      switch (method) {
        case "read":    resp = model.id ? store.find(model) : store.findAll(); break;
        case "create":  resp = store.create(model);                            break;
        case "update":  resp = store.update(model);                            break;
        case "delete":  resp = store.destroy(model);                           break;
      }

      if (resp) {
        success(resp);
      } else {
        error("Record not found");
      }
    };