Firefox-specific patch for HTMLImports polyfill.

firefox-html-imports-patch.js

/**
 * HTML Imports implementation seems to be broken in Firefox.
 * Enabling dom.webcomponents.enabled adds `import` attribute
 * to the HTMLLinkElement. This makes HTMLImports polyfill to
 * fall-back to native implementation.
 * This patch intercepts `document.createElement()` call from
 * the polyfill, thus needs to be loaded before HTMLImports.js.
 * @see https://github.com/webcomponents/webcomponentsjs/issues/289
 * @author mliszcz<liszcz.michal@gmail.com>
 * @license MIT
 */
(function (window, document, console) {
  'use strict'

  // http://stackoverflow.com/questions/9847580/how-to-detect-safari-chrome-ie-firefox-and-opera-browser
  var isFirefox = typeof InstallTrigger !== 'undefined';

  if (isFirefox) {

    console.debug('patching document.createElement for HTMLImports');

    var _createElement = document.createElement;
    var callCount = 0;

    // HTMLImports polyfill creates 'link' element and
    // checks for the presence of 'import' attribute.
    document.createElement = function(...args) {

      var element = _createElement.apply(document, args);

      if (callCount++ == 0 && args[0] == 'link' && 'import' in element) {
        console.debug('returning patched link element');
        return {};
      } else {
        return element;
      }
    };

    window.addEventListener('DOMContentLoaded', function() {
      console.debug('restoring document.createElement');
      document.createElement = _createElement;
    });
  }

})(window, document, console);

package.json

{
  "name": "firefox-html-imports-patch",
  "version": "0.1.0",
  "description": "Patch for HTMLImports polyfill to work with dom.webcomponents.enabled",
  "main": "firefox-html-imports-patch.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "repository": {
    "type": "git",
    "url": "git+https://gist.github.com/d11ea630cc777012d69b.git"
  },
  "keywords": [
    "html",
    "imports",
    "web",
    "components"
  ],
  "author": "mliszcz <liszcz.michal@gmail.com>",
  "license": "MIT",
  "bugs": {
    "url": "https://gist.github.com/d11ea630cc777012d69b"
  },
  "homepage": "https://gist.github.com/d11ea630cc777012d69b"
}