Example Application Cache "Bootloader"

gistfile1.js

(function(){

  function useManifest(content){
    var tag;
    var stylesheets = content.match(/\/css\/.*\.css/g);
    for (var i=0; i<stylesheets.length; i++){
      tag = document.createElement('link');
      tag.href = stylesheets[i];
      tag.rel = "stylesheet";
      document.getElementsByTagName('head')[0].appendChild(tag);
    }
    var scripts = content.match(/\/js\/.*\.js/g);
    var loadedCount = 0;
    function didLoad(){
      loadedCount += 1;
      if (loadedCount == scripts.length){
        var global = (function(){return this;})();
        global.bootloadedManifest = {
          scripts: scripts,
          stylesheets: stylesheets,
          body: content
        };
        require('main');
      }
    }
    for (i=0; i<scripts.length; i++) {
      // This is where you can choose to skip over certain Javascript files 
      // that appear in the manifest -- in this case, a web worker runtime
      if (/\bworker\b/.test(scripts[i])){
        loadedCount +=1;
      } else {
        tag = document.createElement('script');
        tag.src = scripts[i];
        tag.type = "text/javascript";
        tag.onload = didLoad;
        document.getElementsByTagName('head')[0].appendChild(tag);
      }
    }
  }


  function retrieveManifest(cb){
    var req = new XMLHttpRequest();
    req.open("GET",document.documentElement.getAttribute('manifest'),true);
    req.onreadystatechange = function(){
      if (req.readyState === req.DONE){
        if (req.status === 200){
          cb(req.response);
        } else {
          throw new Error("failed to retrieve manifest");
        }
      }
    };
    req.send();
  }

  // In development, you don't want to be running out of an actual 
  // application cache, because you need to reload all the time. But
  // we do want to test everything under the bootloader. So this lets
  // you provide a fake manifest file within a <script type="text/fake-manifest"> 
  // tag.
  function retrieveFakeManifest(cb){
    var content = document.querySelector('script[type="text/fake-manifest"]').innerHTML;
    if (content)
      cb(content);
    else
      throw new Error("no fake manifest available");
  }
  
  if (document.documentElement.getAttribute('manifest')){
    retrieveManifest(useManifest);
  } else {
    retrieveFakeManifest(useManifest);
  }
})();

The HTML5 application cache has its quirks. One of them is that there is a race condition between updating your HTML file (which has references to other assets that appear in the cache manifest) and the cache manifest file. If you end up with skew, your whole app can break.

This example shows a strategy for avoiding the problem. Instead of embedding links to our Javascript and CSS bundles, we dynamically discover them by reading the cache manifest itself. This way you never reference an asset that isn't in the cache.

Looks promising. Have you had many use cases where appcache was very useful in these modern times where internet is readily available?