Backbone sessionStorage Adapter

backbone.sessionStorage.js

/**
 * Backbone sessionStorage Adapter
 * Based on https://github.com/jeromegn/Backbone.localStorage
 */

(function() {
// A simple module to replace `Backbone.sync` with *sessionStorage*-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 *sessionStorage*. Create it
// with a meaningful name, like the name you'd give a table.
// window.Store is deprectated, use Backbone.SessionStorage instead
Backbone.SessionStorage = window.Store = function(name) {
  this.name = name;
  var store = this.sessionStorage().getItem(this.name);
  this.records = (store && store.split(",")) || [];
};

_.extend(Backbone.SessionStorage.prototype, {

  // Save the current state of the **Store** to *sessionStorage*.
  save: function() {
    this.sessionStorage().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.sessionStorage().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.sessionStorage().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) {
    var stored = this.sessionStorage().getItem(this.name+"-"+model.id);
    if(stored) {
      return JSON.parse(stored);
    } else {
      return null;
    }
  },

  // Return the array of all models currently in storage.
  findAll: function() {
    return _(this.records).chain()
        .map(function(id){return JSON.parse(this.sessionStorage().getItem(this.name+"-"+id));}, this)
        .compact()
        .value();
  },

  // Delete a model from `this.data`, returning it.
  destroy: function(model) {
    this.sessionStorage().removeItem(this.name+"-"+model.id);
    this.records = _.reject(this.records, function(record_id){return record_id == model.id.toString();});
    this.save();
    return model;
  },

  sessionStorage: function() {
      return sessionStorage;
  }

});

// sessionSync delegate to the model or collection's
// *sessionStorage* property, which should be an instance of `Store`.
// window.Store.sync and Backbone.sessionSync is deprectated, use Backbone.SessionStorage.sync instead
Backbone.SessionStorage.sync = function(method, model, options, error) {
  var store = model.sessionStorage || model.collection.sessionStorage;

  // Backwards compatibility with Backbone <= 0.3.3
  if (typeof options == 'function') {
    options = {
      success: options,
      error: error
    };
  }

  var resp, syncDfd = $.Deferred();

  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);
    syncDfd.resolve();
  } else {
    if(options.error) {
      options.error("Record not found");
    }
    syncDfd.reject();
  }

  return syncDfd.promise();
};

Backbone.SessionStorage.ajaxSync = Backbone.sync;
Backbone.sessionStorageEnabled = true;

Backbone.bypassSessionStorage = function(obj, func, options) {
  Backbone.sessionStorageEnabled = false;
  var result = func.call(obj, options || {});
  Backbone.sessionStorageEnabled = true;
  return result;
}

Backbone.getSyncMethod = function(model) {
  if((model.sessionStorage || (model.collection && model.collection.sessionStorage)) && Backbone.sessionStorageEnabled)
  {
    return Backbone.SessionStorage.sync;
  }

  return Backbone.SessionStorage.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]);
};

})();

Updated to work with Backbone 1.0 (and dropped backwards compatibility with ancient versions).

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