Backbone.ViewCache

Maintains a cache of Backbone views based on the view’s route fragment. Retains the view’s scroll position by default (useful when re-inserting view elements into the DOM).

Cache expiry can be set globally and per view instance.

Installation

In a browser, include the plugin after jQuery, Underscore (or an equivalent library such as lodash), and Backbone have been included.

<script src="backbone.viewcache.js"></script>

Backbone.ViewCache can also be loaded as an AMD module or required in CommonJS-like environments (like Node) – e.g. for use with RequireJS or Browserify. It can be installed using the Bower package manager.

bower install backbone.viewcache --save

// AMD
require(['backbone.viewcache'], function(ViewCache){ /* ... */ });
// Node.js
var ViewCache = require('backbone.viewcache');

Usage

Use Backbone.ViewCache in your route handlers.

home: function() {
  // Get the cached view for the current URL fragment.
  var homeView = Backbone.ViewCache.get();

  if (homeView) {
    // Re-activate the cached view.
    homeView.delegateEvents();
  } else {
    // Not in cache, instantiate a new view and cache it.
    homeView = Backbone.ViewCache.set(new HomeView());

    homeView.render();
  }

  // (Re-)insert the view element into the DOM.
}

// Remove the view for the current URL fragment from the cache.
Backbone.ViewCache.remove();

// Clear the cache, or clear all expired views from the cache.
Backbone.ViewCache.clear();
Backbone.ViewCache.clearExpireds();

// "get", "set", and "remove" can also be called with an optional URL
// fragment argument. Defaults to `Backbone.history.fragment`.
Backbone.ViewCache.get('search');
Backbone.ViewCache.set(new SearchView(), 'search');
Backbone.ViewCache.remove('search');

For retaining the scroll position and auto-clear expireds functionality, Backbone.ViewCache beforeRoute and afterRoute methods have to be called as pre- and post-route hooks. This can be done in your router’s execute method (added in Backbone v1.0.0).

execute: function(callback, args) {
  Backbone.ViewCache.beforeRoute();
  if (callback) callback.apply(this, args);
  Backbone.ViewCache.afterRoute();
}

Configuration

Configure Backbone.ViewCache globally. Example with default configuration:

Backbone.ViewCache.config({

  // Automatically save and restore the cached view’s scroll position.
  // Useful when re-inserting view elements into the DOM.
  retainScrollPosition: true,

  // Element that will be used for retaining the view’s scroll position.
  // Can be a selector string or DOM element.
  scrollElement: window,

  // Cached view’s expiry time in seconds, or falsy for no expiry.
  // Can be overridden per view with the view’s `setCacheExpiry` method.
  cacheExpiry: undefined,

  // Time in seconds to have Backbone.ViewCache automatically clear
  // expired views from the cache with `Backbone.ViewCache.beforeRoute`.
  // Defaults to the value of the "cacheExpiry" configuration setting.
  checkExpireds: undefined,

  // When restoring the cached view’s scroll position, scroll to the top of
  // `scrollElement` if the view currently has no saved scroll position.
  scrollToTopByDefault: true

});

Methods added to Backbone.View.prototype

Backbone views are extended with three additional methods which are called internally and can also be called on demand: saveScrollPosition, restoreScrollPosition, and setCacheExpiry.

// Expire the view in 5 minutes (takes precedence over global config).
homeView.setCacheExpiry(300);

// While the view is in the DOM, save its scroll position.
homeView.saveScrollPosition();

// While the view is in the DOM, restore its scroll position.
// (Scrolls to top if the "scrollToTopByDefault" setting is on and
//  the view currently has no saved scroll position.)
homeView.restoreScrollPosition();

Limitations

Due to a known Android bug, restoring the view’s scroll position doesn’t work in the stock browser for Android 4.0.x (Ice Cream Sandwich) and lower.