hexo.extend.helper.register("js_cdn", function(item) {
  const js = hexo.extend.helper.get("js").bind(hexo);
  const integrityProp = "integrity";
  const placeholder = " " + integrityProp;
  const crossoriginAttr = ' crossorigin="anonymous"';
  let markup = js(item);
  if (item.hasOwnProperty(integrityProp)) {
    // default `js` helper function doesn't include crossorigin="anonymous" in the generated script markup
    const idx = markup.indexOf(placeholder);
    markup = [markup.substring(0, idx), crossoriginAttr, markup.substring(idx)].join("");
  }
  return markup;
});

(function() {
  var dependencies = [
    {
      export: window.jQuery,
      failover: "https://ajax.aspnetcdn.com/ajax/jQuery/jquery-2.0.3.min.js",
      // failover: "https://code.jquery.com/jquery-2.0.3.min.js",
      integrity: "sha256-sTy1mJ4I/LAjFCCdEB4RAvPSmRCb3CU7YqodohyeOLo="
    },
    {
      export: (window.jQuery || {}).fancybox,
      failover:
        "https://cdnjs.cloudflare.com/ajax/libs/fancybox/2.1.5/jquery.fancybox.pack.js",
      integrity:
        "sha384-A/Tc8RFHsjkPvgL0yZebgTxxmCGCSaTpGkyQLeFFFJQIAzSozLwNGX9AOCIpxoXC"
    }
  ];
  // failover to load alternative files when CDN libraries failed.
  var nonLoadedDependencies = dependencies.filter(function(dep) {
    return !dep.export;
  });
  /** lazy load js files */
  function loadDependency(dep) {
    return new Promise(function(resolve, reject) {
      var script = document.createElement("script");
      script.src = dep.failover;
      if (dep.integrity && dep.integrity.length) {
        script.integrity = dep.integrity;
        script.crossOrigin = "anonymous";
      }
      // // https://www.html5rocks.com/en/tutorials/speed/script-loading/#toc-dom-rescue
      script.async = false;
      script.addEventListener("load", function() {
        resolve(dep.failover + " is loaded");
      });
      script.addEventListener("error", function() {
        reject(dep.failover + " can't be loaded!");
      });
      document.body.appendChild(script);
    });
  }

  (nonLoadedDependencies.length
    ? new Promise(function(resolve, reject) {
        Promise.all(nonLoadedDependencies.map(loadDependency)).then(function() {
          resolve("All dependencies are loaded!");
        }, reject);
      })
    : Promise.resolve("All dependencies are loaded!")
  ).then(myBiz);

  /** business logic, will be executed when all dependencies loaded */
  function myBiz() {
    /// your business code comes here
  }
})();