Backbone fetch cache

A Backbone plugin to cache calls to Backbone.Model.prototype.fetch and Backbone.Collection.prototype.fetch in memory and localStorage.

Compatible with Backbone 1.0.0 and up.

How it works

This plugin intercepts calls to fetch and stores the results in a cache object (Backbone.fetchCache._cache). If fetch is called with { cache: true } in the options and the URL has already been cached the AJAX call will be skipped.

The local cache is persisted in localStorage if available for faster initial page loads.

The prefill option allows for models and collections to be filled with cache data just until the fetch operations are complete -- a nice way to make the app feel snappy on slower connections.

What's wrong with browser caching for AJAX responses?

Nothing. This plugin is primarily for working with an API where you don't have control over response cache headers.

Usage

Add the script to the page after backbone.js has been included:

<script src="/path/to/backbone.js"></script>
<script src="/path/to/backbone.fetch-cache.js"></script>

or if you're using AMD, require the script as a module:

require(['path/to/backbone.fetch-cache.js']);

Note that the AMD module depends on underscore and backbone modules being defined as it lists them as dependencies. If you don't have these mapped, you can do it by adding the following to your require config:

requirejs.config({
  paths: {
    backbone: 'actual/path/to/backbone.js',
    underscore: 'actual/path/to/underscore.js'
  }
});

A note on Zepto.js. This plugin uses jQuery.Deferred which is not included in Zepto. You'll need to add a third party implementation of jQuery.Deferred, e.g. Standalone-Deferred

Options

cache

Calls to modelInstance.fetch or collectionInstance.fetch will be fulfilled from the cache (if possible) when cache: true is set in the options hash:

myModel.fetch({ cache: true });
myCollection.fetch({ cache: true });

---

prefill

This option allows the model/collection to be populated from the cache immediately and then be updated once the call to fetch has completed. The initial cache hit calls the prefillSuccess callback and then the AJAX success/error callbacks are called as normal when the request is complete. This allows the page to render something immediately and then update it after the request completes. (Note: the prefillSuccess callback will not fire if the data is not found in the cache.)

myModel.fetch({
  prefill: true,
  prefillSuccess: someCallback, // Fires when the cache hit happens
  success: anotherCallback // Fires after the AJAX call
});

myCollection.fetch({
  prefill: true,
  prefillSuccess: someCallback, // Fires when the cache hit happens
  success: anotherCallback // Fires after the AJAX call
});

This option can be used with the promises interface like so (note: the progress event will not fire if the data is not found in the cache.):

var modelPromise = myModel.fetch({ prefill: true });
modelPromise.progress(someCallback); // Fires when the cache hit happens
modelPromise.done(anotherCallback); // Fires after the AJAX call

var collectionPromise = myModel.fetch({ prefill: true });
collectionPromise.progress(someCallback); // Fires when the cache hit happens
collectionPromise.done(anotherCallback); // Fires after the AJAX call

---

expires

Cache vales expire after 5 minutes by default. You can adjust this by passing expires: <seconds> to the fetch call. Set to false to never expire:

myModel.fetch({ cache: true, expires: 60000 });
myCollection.fetch({ cache: true, expires: 60000 });

// These will never expire
myModel.fetch({ cache: true, expires: false });
myCollection.fetch({ cache: true, expires: false });

---

localStorage

By default the cache is persisted in localStorage (if available). Set Backbone.fetchCache.localStorage = false to disable this:

Backbone.fetchCache.localStorage = false;

Custom cache keys

By default the cache key is generated from the model's url property and the requests params:

'/model/1?some=param'

This can be overridden with custom logic if required:

// Instance is a Backbone.Model or Backbone.Collection, options are passed
// through form the fetch call
Backbone.fetchCache.getCacheKey = function(instance, options) {
  return instance.constructor.name + ':' + instance.get('id');
  // => UserModel:1
};

priorityFn

When setting items in localStorage, the browser may throw a QUOTA_EXCEEDED_ERR, meaning the store is full. Backbone.fetchCache tries to work around this problem by deleting what it considers the most stale item to make space for the new data. The staleness of data is determined by the sorting function ```priorityFn````, which by default returns the oldest item.

The default is:

Backbone.fetchCache.priorityFn = function(a, b) {
  if (!a || !a.expires || !b || !b.expires) {
    return a;
  }

  return a.expires - b.expires;
};

You can override this function with your own logic (in this case, returning the most recent item):

Backbone.fetchCache.priorityFn = function(a, b) {
  return b.expires - a.expires;
};

Events

The sync event is triggered on a cache hit. A cachesync event is also triggered on Models and Collections, but only when a cache hit happens. This can be used if you need to differentiate between a server backed sync event and a cache backed event.

Automatic cache invalidation

The cache item for a particular call will be cleared when a create, update, patch or delete call is made to the server. The plugin tries to be intelligent about this by clearing a model's collection cache if the model has a .collection property.

To achieve this, the plugin overrides Backbone.Model.protoype.sync and then calls the original method. If you are planning to override sync on a particular model then you should keep this in mind and make sure that you do it before the plugin runs. Overriding Backbone.sync directly should work fine.

Manual cache invalidation

Sometimes you just need to clear a cached item manually. This can be called safely from anywhere in your application.

Backbone.fetchCache.clearItem(myModel.url);

Tests

You can run the tests by cloning the repo, installing the dependencies and running grunt jasmine:

$ npm install
$ grunt jasmine

The default grunt task runs tests and lints the code.

$ grunt