boomerangjs/plugins/cache-test-plugin.js

boomerang always comes back, except when it hits something

/**
 * The `CT` plugin tests how long an item stays in the browser's cache.
 *
 * Given a URL, this plugin loads the specified URL and measures how long it took to load.
 *
 * You can use the results of this plugin to determine how cacheable a URL is across
 * browsers and over time.
 *
 * For information on how to include this plugin, see the {@tutorial building} tutorial.
 *
 * ## Usage
 *
 * This plugin requires a server-generated JavaScript file that calls
 * {@link BOOMR.plugins.CT.loaded} with the server's timestamp.
 *
 * This file is specified as {@link BOOMR.plugins.CT.init CT.cached_url} and should
 * return an `application/javascript` file with contents similar to:
 *
 * ```
 * BOOMR.plugins.CT.loaded(12345); // server-generated timestamp
 * ```
 *
 * ## Beacon Parameters
 *
 * This plugin adds the following parameters to the beacon:
 *
 * * `cch.ce`: Time when the cached item started to load
 * * `cch.lt`: Load time of cached item (ms)
 * * `cch.se`: Server timestamp
 *
 * @class BOOMR.plugins.CT
 */
(function() {
  var dc = document,
      s = "script",
      dom = location.hostname,
      complete = false,
      t_start;

  BOOMR = window.BOOMR || {};
  BOOMR.plugins = BOOMR.plugins || {};

  if (BOOMR.plugins.CT) {
    return;
  }

  // Don't even bother creating the plugin if this is mhtml
  if (!dom ||
    dom === "localhost" ||
    dom.match(/\.\d+$/) ||
    dom.match(/^mhtml/) ||
    dom.match(/^file:\//)) {
    return;
  }

  /**
   * Loads the cache URL
   */
  function load() {
    var s0 = dc.getElementsByTagName(s)[0],
        s1 = dc.createElement(s);

    s1.onload = BOOMR.plugins.CT.loaded;
    s1.src = cached_url;
    t_start = BOOMR.now();
    BOOMR.addVar("cch.ce", t_start);

    s0.parentNode.insertBefore(s1, s0);
    s0 = s1 = null;

    // this is a timeout so we don't wait forever to send the beacon
    // if the server fails
    setTimeout(BOOMR.plugins.CT.loaded, 500);
  };

  //
  // Exports
  //
  BOOMR.plugins.CT = {
    /**
     * Initializes the plugin.
     *
     * @param {object} config Configuration
     * @param {string} config.CT.cached_url URL to load
     *
     * @returns {@link BOOMR.plugins.CT} The CT plugin for chaining
     * @memberof BOOMR.plugins.CT
     */
    init: function(config) {
      if (complete) {
        return this;
      }

      if (config && config.CT && config.CT.cached_url) {
        cached_url = config.CT.cached_url;
      }
      else {
        complete = true;

        return this;
      }

      if (BOOMR.window === window) {
        BOOMR.subscribe("page_ready", load, null, null);
      }
      else {
        load();
      }

      return this;
    },

    /**
     * This plugin is always complete (ready to send a beacon)
     *
     * @returns {boolean} `true`
     * @memberof BOOMR.plugins.CACHE_RELOAD
     */
    is_complete: function() {
      return complete;
    },

    /**
     * Called when the {@link BOOMR.plugins.CT.init CT.cached_url} is loaded.
     *
     * @param {number} t Server timestamp
     */
    loaded: function(t) {
      if (complete) {
        return;
      }

      if (!t) {
        t = -1;
      }

      // how long did it take for the call to return
      BOOMR.addVar({
        "cch.lt": BOOMR.now() - t_start,
        "cch.se": t
      });

      complete = true;
      BOOMR.sendBeacon();
    }
  };
}());