# backbone-localstorage.js

    /**
     * Backbone localStorage Adapter
     * https://github.com/jeromegn/Backbone.localStorage
     */

    (function() {

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

Hold reference to Underscore.js and Backbone.js in the closure in order to make things work even if they are removed from the global namespace

    var _ = this._;
    var Backbone = this.Backbone;

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. window.Store is deprectated, use Backbone.LocalStorage instead

    Backbone.LocalStorage = window.Store = function(name) {
      this.name = name;
      var store = this.localStorage().getItem(this.name);
      this.records = (store && store.split(",")) || [];
    };

    _.extend(Backbone.LocalStorage.prototype, {

Save the current state of the Store to localStorage.

      save: function() {
        this.localStorage().setItem(this.name, this.records.join(","));
      },

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 = guid();
            model.set(model.idAttribute, model.id);
        }
        this.localStorage().setItem(this.name+"-"+model.id, JSON.stringify(model));
        this.records.push(model.id.toString());
        this.save();
        return model.toJSON();
      },

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

      update: function(model) {
        this.localStorage().setItem(this.name+"-"+model.id, JSON.stringify(model));
        if (!_.include(this.records, model.id.toString())) this.records.push(model.id.toString()); this.save();
        return model.toJSON();
      },

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

      find: function(model) {
        return JSON.parse(this.localStorage().getItem(this.name+"-"+model.id));
      },

Return the array of all models currently in storage.

      findAll: function() {
        return _(this.records).chain()
            .map(function(id){return JSON.parse(this.localStorage().getItem(this.name+"-"+id));}, this)
            .compact()
            .value();
      },

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

      destroy: function(model) {
        this.localStorage().removeItem(this.name+"-"+model.id);
        this.records = _.reject(this.records, function(record_id){return record_id == model.id.toString();});
        this.save();
        return model;
      },

      localStorage: function() {
          return localStorage;
      }

    });

localSync delegate to the model or collection's localStorage property, which should be an instance of `Store`. window.Store.sync and Backbone.localSync is deprectated, use Backbone.LocalStorage.sync instead

    Backbone.LocalStorage.sync = window.Store.sync = Backbone.localSync = function(method, model, options, error) {
      var store = model.localStorage || model.collection.localStorage;

Backwards compatibility with Backbone <= 0.3.3

      if (typeof options == 'function') {
        options = {
          success: options,
          error: error
        };
      }

      var resp;

      switch (method) {
        case "read":    resp = model.id != undefined ? 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) {
        options.success(resp);
      } else {
        options.error('Record not found.');
      }
    };

    Backbone.ajaxSync = Backbone.sync;

    Backbone.getSyncMethod = function(model) {
      if(model.localStorage || (model.collection && model.collection.localStorage))
      {
        return Backbone.localSync;
      }

      return Backbone.ajaxSync;
    };

Override 'Backbone.sync' to default to localSync, the original 'Backbone.sync' is still available in 'Backbone.ajaxSync'

    Backbone.sync = function(method, model, options, error) {
      return Backbone.getSyncMethod(model).apply(this, [method, model, options, error]);
    };

    })();

h