←  offliner-updater-reinstall.js
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How to write an update implementation
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Remember including offliner will export the off module with a namespace reserved for updaters. Put your update implementation inside.

 
self.off.updaters.reinstall = {
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Should check for the latest version. It must return a promise resolving with a version tag, which is a string representing the version.

 
  check: function () {
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For this demo we are checking the hash of the HEAD of gh-pages branch on GitHub. We will use the free GitHub API for that end.

 
    var ghInfo = this.getGHInfoFromGHPages(self.location);
    var path = [
      'repos', ghInfo.username, ghInfo.repo, 'commits', 'gh-pages'
    ].join('/');
    var updateChannel = 'https:
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api.github.com/' + path;
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Once we know the API URL, simply fetch and extract the hash field from the response.

 
    return fetch(updateChannel).then(function (response) {
      if (response.status === 200) {
        return response.json().then(function (body) {
          return Promise.resolve('v' + body.sha);
        });
      }
      else {
        throw new Error('Can not check for new version: ' + response.status);
      }
    });
  },
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Should check if the version from the step above is a new version given the current one. Notice offliner is not aware about the meaning of your versions but you could write middleware understanding semver for instance.

 
  isNewVersion: function (current, latest) {
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The update process set some flags you can check in the flags property. Flag isFirstUpdate indicates the worker has triggered the update strategy for the first time.

 
    return this.flags.isFirstUpdate ||
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We have a new version every time the hash changes.

 
           current !== latest;
  },
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Should implement how to update the current cache.

 
  evolve: function (previousCache, newCache, reinstall) {
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The callback reinstall is provided to trigger a prefetch directly on the new cache. Several times, the only thing you need to do in order to update is to reinstall all again.

 
    return reinstall();
  },
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Of course you can provide as many extra functions as you need.

 
  getGHInfoFromGHPages: function (url) {
    return {
      username: url.host.split('.')[0],
      repo: url.pathname.split('/')[1]
    };
  }
};