Function patchShadowDom

build-system/common/update-packages.js:113–180

* Patches Shadow DOM polyfill by wrapping its body into `install` * function. * This gives us an option to control when and how the polyfill is installed. * The polyfill can only be installed on the root context.

()

 * The polyfill can only be installed on the root context.
 */
function patchShadowDom() {
  // Copies webcomponents-sd into a new file that has an export.
  const patchedName =
    'node_modules/@webcomponents/webcomponentsjs/bundles/webcomponents-sd.install.js';

  let file = '(function() {';
  // HTMLElement is replaced, but the original needs to be used for the polyfill
  // since it manipulates "own" properties. See `src/polyfills/custom-element.js`.
  file += 'var HTMLElementOrig = window.HTMLElementOrig || window.HTMLElement;';
  file += 'window.HTMLElementOrig = HTMLElementOrig;';
  file += `
    (function() {
      var origContains = document.contains;
      if (origContains) {
        Object.defineProperty(document, '__shady_native_contains', {value: origContains});
      }
      Object.defineProperty(document, 'contains', {
        configurable: true,
        value: function(node) {
          if (node === this) {
            return true;
          }
          if (this.documentElement) {
            return this.documentElement.contains(node);
          }
          return false;
        }
      });
    })();
  `;

  /**
   * @param {string} file
   * @return {string}
   */
  function transformScript(file) {
    // Use the HTMLElement from above.
    file = file.replace(/\bHTMLElement\b/g, 'HTMLElementOrig');
    return file;
  }

  // Relevant DOM polyfills
  file += transformScript(
    fs
      .readFileSync(
        'node_modules/@webcomponents/webcomponentsjs/bundles/webcomponents-pf_dom.js'
      )
      .toString()
  );
  file += transformScript(
    fs
      .readFileSync(
        'node_modules/@webcomponents/webcomponentsjs/bundles/webcomponents-sd.js'
      )
      .toString()
  );
  file += '})();';