Attempt at refactor for performance gainz

lazy-imports-import.html

<!--
@license
Copyright (c) 2016 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
-->

<script>
  (function() {
    'use strict';

    // var __importPromises = new Map();
    const __lazyImports = new Map();

    function requestImport(link, fromElement, importStatuses) {
      const href = link.getAttribute('href');

      link.promise = new Promise(function(resolve, reject) {
        const importHref = Polymer.importHref || fromElement.importHref;
        importHref(fromElement.resolveUrl(href), resolve, reject);
      });

      return link.promise.then(
        function onLoad() {
          return importStatuses.loaded.push({loaded: href});
        },
        function onFail() {
          return importStatuses.failed.push({failed: href});
        }
      )
    }

    /**
     * Calls `Polymer.Base.importHref` for each `<link rel="lazy-import"` in
     * the `dom-module` where the calling element is defined, where the
     * "group" attribute matches the provided "group". If no group is
     * provided, Lazy HTML Imports with no group will be imported.
     *
     * `importHref` is only called once per globally-unique URL.
     *
     * @param {HTMLElement} fromElement The element to search for lazy imports
     *                                  within.
     * @param {string=} group The group attribute to filter on.
     * @param {object=} options Accepts a retry flag which will force a
     *                          retry of a previously failed import.
     * @return {Promise}
     */
    Polymer.__importLazyGroup = function(fromElement, group, options) {
      // var groupAttribute = group ? '[group="' + group + '"]' : ':not([group])';
      const query =
        'link[rel=\'lazy-import\']' + (group ? '[group]' : ':not([group])') + '[href]:not([href=\'\'])';

      if (!__lazyImports.get(fromElement)) {
        const links =
        Array.from(Polymer.DomModule.import(fromElement.localName).querySelectorAll(query));
        __lazyImports.set(fromElement, links.reduce((obj, link) => {
          const group = link.getAttribute('group');
          if (!obj[group]) {
            obj[group] = [];
          }
          obj[group].push(link);
          return obj;
        }, {}));
      }

      const groupLinks = __lazyImports.get(fromElement)[group];

      if (groupLinks.length < 1) {
        return Promise.reject(
          new Error('No imports found in the specified group.'));
      }

      const __importStatuses = {loaded: [], failed: []};
      const requestPromises = groupLinks.map(function(link) {
        let promise;

        if (link.promise) {
          promise = link.promise;
          if (options && options.retry) {
            promise = promise.catch(requestImport.bind(this, link, fromElement, __importStatuses));
          }
        } else {
          promise = requestImport(link, fromElement, __importStatuses);
        }
        
        return promise;
      });

      return Promise.all(requestPromises).then(function() {
        if (__importStatuses.failed.length > 0) {
          const error = new Error('One or more imports failed to load.');
          error.importStatuses = __importStatuses;
          throw error;
        } else {
          return __importStatuses;
        }
      });
    };
  })();
</script>

profiling-marks.html

<!--
@license
Copyright (c) 2016 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
-->

<script>
  (function() {
    'use strict';

    const __lazyImports = new Map();

    function requestImport(link, fromElement, importStatuses) {
      performance.mark('requestImport');
      const href = link.getAttribute('href');

      link.promise = new Promise(function(resolve, reject) {
        const importHref = Polymer.importHref || fromElement.importHref;
        importHref(fromElement.resolveUrl(href), resolve, reject);
      });

      return link.promise.then(
        function onLoad() {
          performance.mark('loaded');
          return importStatuses.loaded.push({loaded: href});
        },
        function onFail() {
          performance.mark('failed');
          return importStatuses.failed.push({failed: href});
        }
      )
    }

    /**
     * Calls `Polymer.Base.importHref` for each `<link rel="lazy-import"` in
     * the `dom-module` where the calling element is defined, where the
     * "group" attribute matches the provided "group". If no group is
     * provided, Lazy HTML Imports with no group will be imported.
     *
     * `importHref` is only called once per globally-unique URL.
     *
     * @param {HTMLElement} fromElement The element to search for lazy imports
     *                                  within.
     * @param {string=} group The group attribute to filter on.
     * @param {object=} options Accepts a retry flag which will force a
     *                          retry of a previously failed import.
     * @return {Promise}
     */
    Polymer.__importLazyGroup = function(fromElement, group, options) {
      performance.mark('__importLazyGroup-START');
      const query =
        'link[rel=\'lazy-import\']' + (group ? '[group]' : ':not([group])') + '[href]:not([href=\'\'])';

      if (!__lazyImports.get(fromElement)) {
        performance.mark('initializeLazyGroups');
        const links =
        Array.from(Polymer.DomModule.import(fromElement.localName).querySelectorAll(query));
        __lazyImports.set(fromElement, links.reduce((obj, link) => {
          const group = link.getAttribute('group');
          if (!obj[group]) {
            obj[group] = [];
          }
          obj[group].push(link);
          return obj;
        }, {}));
        performance.mark('endLazyGroupInit');
      }

      const groupLinks = __lazyImports.get(fromElement)[group];

      if (groupLinks.length < 1) {
        return Promise.reject(
          new Error('No imports found in the specified group.'));
      }

      const __importStatuses = {loaded: [], failed: []};
      performance.mark('Start-promise-map');
      const requestPromises = groupLinks.map(function(link) {
        let promise;

        if (link.promise) {
          performance.mark('Promise-exists');
          promise = link.promise;
          if (options && options.retry) {
            promise = promise.catch(requestImport.bind(this, link, fromElement, __importStatuses));
          }
        } else {
          performance.mark('new Promise');
          promise = requestImport(link, fromElement, __importStatuses);
        }
        
        return promise;
      });
      performance.mark('End-promise-map');

      return Promise.all(requestPromises).then(function() {
        if (__importStatuses.failed.length > 0) {
          const error = new Error('One or more imports failed to load.');
          error.importStatuses = __importStatuses;
          throw error;
        } else {
          performance.mark('__importLazyGroup-END');
          performance.measure('Total import', '__importLazyGroup-START', '__importLazyGroup-END');
          performance.measure('init', 'initializeLazyGroups', 'endLazyGroupInit');
          performance.measure('map', 'Start-promise-map', 'End-promise-map');
          try {
            performance.measure('Promise exists', 'Promise-exists', '__importLazyGroup-END');
          } catch (ex) {}
          performance.measure('New Promise', 'new Promise', '__importLazyGroup-END');
          performance.measure('requestImport', 'requestImport', 'loaded');
          return __importStatuses;
        }
      });
    };
  })();
</script>