webcomponentsjs/webcomponents-lite.js

/**
 * @license
 * Copyright (c) 2014 The Polymer Project Authors. All rights reserved.
 * This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
 * The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
 * The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
 * Code distributed by Google as part of the polymer project is also
 * subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
 */

(function() {
  // Establish scope.
  window.WebComponents = window.WebComponents || {flags:{}};

  // loading script
  var file = 'webcomponents-lite.js';
  var script = document.querySelector('script[src*="' + file + '"]');

  // Flags. Convert url arguments to flags
  var flags = {};
  if (!flags.noOpts) {
    // from url
    location.search.slice(1).split('&').forEach(function(option) {
      var parts = option.split('=');
      var match;
      if (parts[0] && (match = parts[0].match(/wc-(.+)/))) {
        flags[match[1]] = parts[1] || true;
      }
    });
    // from script
    if (script) {
      for (var i=0, a; (a=script.attributes[i]); i++) {
        if (a.name !== 'src') {
          flags[a.name] = a.value || true;
        }
      }
    }
    // log flags
    if (flags.log && flags.log.split) {
      var parts = flags.log.split(',');
      flags.log = {};
      parts.forEach(function(f) {
        flags.log[f] = true;
      });
    } else {
      flags.log = {};
    }
  }

  // exports
  WebComponents.flags = flags;
  
  // Feature detect which polyfill needs to be imported.
  let polyfills = [];
  if (!('import' in document.createElement('link'))) {
    polyfills.push('hi');
  }
  if (!window.customElements) {
    polyfills.push('ce');
  }
  if (!('attachShadow' in Element.prototype)) {
    polyfills.push('sd');
  }
  if (!('content' in document.createElement('template')) || !window.Promise || !window.URL) {
    polyfills.push('pf');
  }

  // TODO(notwaldorf): This is a temporary hack because of pre/post-polyfill.js,
  // and needs to not exist at all.
  if (!polyfills.length) {
    polyfills.push('none');
  }
  if (polyfills.length) {
    let script = document.createElement('script');
    script.src = `../webcomponents-${polyfills.join('-')}.min.js`;
    console.log('Loaded: ', script.src);
    document.head.appendChild(script);
  }
})();