element-mixin.html

<!--
@license
Copyright (c) 2017 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
-->

<link rel="import" href="../utils/boot.html">
<link rel="import" href="../utils/settings.html">
<link rel="import" href="../utils/mixin.html">
<link rel="import" href="../utils/case-map.html">
<link rel="import" href="../utils/style-gather.html">
<link rel="import" href="../utils/resolve-url.html">
<link rel="import" href="../elements/dom-module.html">
<link rel="import" href="property-effects.html">

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

  /**
   * Element class mixin that provides the core API for Polymer's meta-programming
   * features including template stamping, data-binding, attribute deserialization,
   * and property change observation.
   *
   * Subclassers may provide the following static getters to return metadata
   * used to configure Polymer's features for the class:
   *
   * - `static get is()`: When the template is provided via a `dom-module`,
   *   users should return the `dom-module` id from a static `is` getter.  If
   *   no template is needed or the template is provided directly via the
   *   `template` getter, there is no need to define `is` for the element.
   *
   * - `static get template()`: Users may provide the template directly (as
   *   opposed to via `dom-module`) by implementing a static `template` getter.
   *   The getter may return an `HTMLTemplateElement` or a string, which will
   *   automatically be parsed into a template.
   *
   * - `static get properties()`: Should return an object describing
   *   property-related metadata used by Polymer features (key: property name
   *   value: object containing property metadata). Valid keys in per-property
   *   metadata include:
   *   - `type` (String|Number|Object|Array|...): Used by
   *     `attributeChangedCallback` to determine how string-based attributes
   *     are deserialized to JavaScript property values.
   *   - `notify` (boolean): Causes a change in the property to fire a
   *     non-bubbling event called `<property>-changed`. Elements that have
   *     enabled two-way binding to the property use this event to observe changes.
   *   - `readOnly` (boolean): Creates a getter for the property, but no setter.
   *     To set a read-only property, use the private setter method
   *     `_setProperty(property, value)`.
   *   - `observer` (string): Observer method name that will be called when
   *     the property changes. The arguments of the method are
   *     `(value, previousValue)`.
   *   - `computed` (string): String describing method and dependent properties
   *     for computing the value of this property (e.g. `'computeFoo(bar, zot)'`).
   *     Computed properties are read-only by default and can only be changed
   *     via the return value of the computing method.
   *
   * - `static get observers()`: Array of strings describing multi-property
   *   observer methods and their dependent properties (e.g.
   *   `'observeABC(a, b, c)'`).
   *
   * The base class provides default implementations for the following standard
   * custom element lifecycle callbacks; users may override these, but should
   * call the super method to ensure
   * - `constructor`: Run when the element is created or upgraded
   * - `connectedCallback`: Run each time the element is connected to the
   *   document
   * - `disconnectedCallback`: Run each time the element is disconnected from
   *   the document
   * - `attributeChangedCallback`: Run each time an attribute in
   *   `observedAttributes` is set or removed (note: this element's default
   *   `observedAttributes` implementation will automatically return an array
   *   of dash-cased attributes based on `properties`)
   *
   * @mixinFunction
   * @polymer
   * @appliesMixin Polymer.PropertyEffects
   * @memberof Polymer
   * @property rootPath {string} Set to the value of `Polymer.rootPath`,
   *   which defaults to the main document path
   * @property importPath {string} Set to the value of the class's static
   *   `importPath` property, which defaults to the path of this element's
   *   `dom-module` (when `is` is used), but can be overridden for other
   *   import strategies.
   * @summary Element class mixin that provides the core API for Polymer's
   * meta-programming features.
   */
  Polymer.ElementMixin = Polymer.dedupingMixin(base => {

    /**
     * @constructor
     * @extends {base}
     * @implements {Polymer_PropertyEffects}
     */
    const polymerElementBase = Polymer.PropertyEffects(base);

    let caseMap = Polymer.CaseMap;

    /**
     * Returns the `properties` object specifically on `klass`. Use for:
     * (1) super chain mixes togther to make `propertiesForClass` which is
     * then used to make `observedAttributes`.
     * (2) properties effects and observers are created from it at `finalize` time.
     *
     * @param {HTMLElement} klass Element class
     * @return {Object} Object containing own properties for this class
     * @private
     */
    function ownPropertiesForClass(klass) {
      if (!klass.hasOwnProperty(
        JSCompiler_renameProperty('__ownProperties', klass))) {
        klass.__ownProperties =
          klass.hasOwnProperty(JSCompiler_renameProperty('properties', klass)) ?
          /** @type PolymerElementConstructor */ (klass).properties : {};
      }
      return klass.__ownProperties;
    }

    /**
     * Returns the `observers` array specifically on `klass`. Use for
     * setting up observers.
     *
     * @param {HTMLElement} klass Element class
     * @return {Array} Array containing own observers for this class
     * @private
     */
    function ownObserversForClass(klass) {
      if (!klass.hasOwnProperty(
        JSCompiler_renameProperty('__ownObservers', klass))) {
        klass.__ownObservers =
          klass.hasOwnProperty(JSCompiler_renameProperty('observers', klass)) ?
          /** @type PolymerElementConstructor */ (klass).observers : [];
      }
      return klass.__ownObservers;
    }

    /**
     * Mixes `props` into `flattenedProps` but upgrades shorthand type
     * syntax to { type: Type}.
     *
     * @param {Object} flattenedProps Bag to collect flattened properties into
     * @param {Object} props Bag of properties to add to `flattenedProps`
     * @return {Object} The input `flattenedProps` bag
     * @private
     */
    function flattenProperties(flattenedProps, props) {
      for (let p in props) {
        let o = props[p];
        if (typeof o == 'function') {
          o = { type: o };
        }
        flattenedProps[p] = o;
      }
      return flattenedProps;
    }

    /**
     * Returns a flattened list of properties mixed together from the chain of all
     * constructor's `config.properties`. This list is used to create
     * (1) observedAttributes,
     * (2) class property default values
     *
     * @param {PolymerElementConstructor} klass Element class
     * @return {PolymerElementProperties} Flattened properties for this class
     * @suppress {missingProperties} class.prototype is not a property for some reason?
     * @private
     */
    function propertiesForClass(klass) {
      if (!klass.hasOwnProperty(
        JSCompiler_renameProperty('__classProperties', klass))) {
        klass.__classProperties =
        flattenProperties({}, ownPropertiesForClass(klass));
        let superCtor = Object.getPrototypeOf(klass.prototype).constructor;
        if (superCtor.prototype instanceof PolymerElement) {
          klass.__classProperties = Object.assign(
            Object.create(propertiesForClass(/** @type PolymerElementConstructor */(superCtor))),
            klass.__classProperties);
        }
      }
      return klass.__classProperties;
    }

    /**
     * Returns a list of properties with default values.
     * This list is created as an optimization since it is a subset of
     * the list returned from `propertiesForClass`.
     * This list is used in `_initializeProperties` to set property defaults.
     *
     * @param {PolymerElementConstructor} klass Element class
     * @return {PolymerElementProperties} Flattened properties for this class
     *   that have default values
     * @private
     */
    function propertyDefaultsForClass(klass) {
      if (!klass.hasOwnProperty(
        JSCompiler_renameProperty('__classPropertyDefaults', klass))) {
        klass.__classPropertyDefaults = null;
        let props = propertiesForClass(klass);
        for (let p in props) {
          let info = props[p];
          if ('value' in info) {
            klass.__classPropertyDefaults = klass.__classPropertyDefaults || {};
            klass.__classPropertyDefaults[p] = info;
          }
        }
      }
      return klass.__classPropertyDefaults;
    }

    /**
     * Returns true if a `klass` has finalized. Called in `ElementClass.finalize()`
     * @param {PolymerElementConstructor} klass Element class
     * @return {boolean} True if all metaprogramming for this class has been
     *   completed
     * @private
     */
    function hasClassFinalized(klass) {
      return klass.hasOwnProperty(JSCompiler_renameProperty('__finalized', klass));
    }

    /**
     * Called by `ElementClass.finalize()`. Ensures this `klass` and
     * *all superclasses* are finalized by traversing the prototype chain
     * and calling `klass.finalize()`.
     *
     * @param {PolymerElementConstructor} klass Element class
     * @private
     */
    function finalizeClassAndSuper(klass) {
      let proto = /** @type PolymerElementConstructor */ (klass).prototype;
      let superCtor = Object.getPrototypeOf(proto).constructor;
      if (superCtor.prototype instanceof PolymerElement) {
        superCtor.finalize();
      }
      finalizeClass(klass);
    }

    /**
     * Configures a `klass` based on a staic `klass.config` object and
     * a `template`. This includes creating accessors and effects
     * for properties in `config` and the `template` as well as preparing the
     * `template` for stamping.
     *
     * @param {PolymerElementConstructor} klass Element class
     * @private
     */
    function finalizeClass(klass) {
      klass.__finalized = true;
      let proto = /** @type PolymerElementConstructor */ (klass).prototype;
      if (klass.hasOwnProperty(
        JSCompiler_renameProperty('is', klass)) && klass.is) {
        Polymer.telemetry.register(proto);
      }
      let props = ownPropertiesForClass(klass);
      if (props) {
        finalizeProperties(proto, props);
      }
      let observers = ownObserversForClass(klass);
      if (observers) {
        finalizeObservers(proto, observers, props);
      }
      // note: create "working" template that is finalized at instance time
      let template = /** @type PolymerElementConstructor */ (klass).template;
      if (template) {
        if (typeof template === 'string') {
          let t = document.createElement('template');
          t.innerHTML = template;
          template = t;
        } else {
          template = template.cloneNode(true);
        }
        proto._template = template;
      }
    }

    /**
     * Configures a `proto` based on a `properties` object.
     * Leverages `PropertyEffects` to create property accessors and effects
     * supporting, observers, reflecting to attributes, change notification,
     * computed properties, and read only properties.
     * @param {PolymerElement} proto Element class prototype to add accessors
     *    and effects to
     * @param {Object} properties Flattened bag of property descriptors for
     *    this class
     * @private
     */
    function finalizeProperties(proto, properties) {
      for (let p in properties) {
        createPropertyFromConfig(proto, p, properties[p], properties);
      }
    }

    /**
     * Configures a `proto` based on a `observers` array.
     * Leverages `PropertyEffects` to create observers.
     * @param {PolymerElement} proto Element class prototype to add accessors
     *   and effects to
     * @param {Object} observers Flattened array of observer descriptors for
     *   this class
     * @param {Object} dynamicFns Object containing keys for any properties
     *   that are functions and should trigger the effect when the function
     *   reference is changed
     * @private
     */
    function finalizeObservers(proto, observers, dynamicFns) {
      for (let i=0; i < observers.length; i++) {
        proto._createMethodObserver(observers[i], dynamicFns);
      }
    }

    /**
     * Creates effects for a property.
     *
     * Note, once a property has been set to
     * `readOnly`, `computed`, `reflectToAttribute`, or `notify`
     * these values may not be changed. For example, a subclass cannot
     * alter these settings. However, additional `observers` may be added
     * by subclasses.
     *
     * The info object should may contain property metadata as follows:
     *
     * * `type`: {function} type to which an attribute matching the property
     * is deserialized. Note the property is camel-cased from a dash-cased
     * attribute. For example, 'foo-bar' attribute is dersialized to a
     * property named 'fooBar'.
     *
     * * `readOnly`: {boolean} creates a readOnly property and
     * makes a private setter for the private of the form '_setFoo' for a
     * property 'foo',
     *
     * * `computed`: {string} creates a computed property. A computed property
     * also automatically is set to `readOnly: true`. The value is calculated
     * by running a method and arguments parsed from the given string. For
     * example 'compute(foo)' will compute a given property when the
     * 'foo' property changes by executing the 'compute' method. This method
     * must return the computed value.
     *
     * * `reflectToAttriute`: {boolean} If true, the property value is reflected
     * to an attribute of the same name. Note, the attribute is dash-cased
     * so a property named 'fooBar' is reflected as 'foo-bar'.
     *
     * * `notify`: {boolean} sends a non-bubbling notification event when
     * the property changes. For example, a property named 'foo' sends an
     * event named 'foo-changed' with `event.detail` set to the value of
     * the property.
     *
     * * observer: {string} name of a method that runs when the property
     * changes. The arguments of the method are (value, previousValue).
     *
     * Note: Users may want control over modifying property
     * effects via subclassing. For example, a user might want to make a
     * reflectToAttribute property not do so in a subclass. We've chosen to
     * disable this because it leads to additional complication.
     * For example, a readOnly effect generates a special setter. If a subclass
     * disables the effect, the setter would fail unexpectedly.
     * Based on feedback, we may want to try to make effects more malleable
     * and/or provide an advanced api for manipulating them.
     * Also consider adding warnings when an effect cannot be changed.
     *
     * @param {PolymerElement} proto Element class prototype to add accessors
     *   and effects to
     * @param {string} name Name of the property.
     * @param {Object} info Info object from which to create property effects.
     * Supported keys:
     * @param {Object} allProps Flattened map of all properties defined in this
     *   element (including inherited properties)
     * @private
     */
    function createPropertyFromConfig(proto, name, info, allProps) {
      // computed forces readOnly...
      if (info.computed) {
        info.readOnly = true;
      }
      // Note, since all computed properties are readOnly, this prevents
      // adding additional computed property effects (which leads to a confusing
      // setup where multiple triggers for setting a property)
      // While we do have `hasComputedEffect` this is set on the property's
      // dependencies rather than itself.
      if (info.computed  && !proto._hasReadOnlyEffect(name)) {
        proto._createComputedProperty(name, info.computed, allProps);
      }
      if (info.readOnly && !proto._hasReadOnlyEffect(name)) {
        proto._createReadOnlyProperty(name, !info.computed);
      }
      if (info.reflectToAttribute && !proto._hasReflectEffect(name)) {
        proto._createReflectedProperty(name);
      }
      if (info.notify && !proto._hasNotifyEffect(name)) {
        proto._createNotifyingProperty(name);
      }
      // always add observer
      if (info.observer) {
        proto._createPropertyObserver(name, info.observer, allProps[info.observer]);
      }
    }

    /**
     * Configures an element `proto` to function with a given `template`.
     * The element name `is` and extends `ext` must be specified for ShadyCSS
     * style scoping.
     *
     * @param {PolymerElement} proto Element class prototype to add accessors
     *   and effects to
     * @param {!HTMLTemplateElement} template Template to process and bind
     * @param {string} baseURI URL against which to resolve urls in
     *   style element cssText
     * @param {string} is Tag name (or type extension name) for this element
     * @param {string=} ext For type extensions, the tag name that was extended
     * @private
     */
    function finalizeTemplate(proto, template, baseURI, is, ext) {
      // support `include="module-name"`
      let cssText =
        Polymer.StyleGather.cssFromModuleImports(is) +
        Polymer.StyleGather.cssFromTemplate(template, baseURI);
      if (cssText) {
        let style = document.createElement('style');
        style.textContent = cssText;
        template.content.insertBefore(style, template.content.firstChild);
      }
      if (window.ShadyCSS) {
        window.ShadyCSS.prepareTemplate(template, is, ext);
      }
      proto._bindTemplate(template);
    }

    /**
     * @polymer
     * @mixinClass
     * @unrestricted
     * @implements {Polymer_ElementMixin}
     */
    class PolymerElement extends polymerElementBase {

      /**
       * Standard Custom Elements V1 API.  The default implementation returns
       * a list of dash-cased attributes based on a flattening of all properties
       * declared in `static get properties()` for this element and any
       * superclasses.
       *
       * @return {Array} Observed attribute list
       */
      static get observedAttributes() {
        if (!this.hasOwnProperty(JSCompiler_renameProperty('__observedAttributes', this))) {
          let list = [];
          let properties = propertiesForClass(this);
          for (let prop in properties) {
            list.push(Polymer.CaseMap.camelToDashCase(prop));
          }
          this.__observedAttributes = list;
        }
        return this.__observedAttributes;
      }

      /**
       * Called automatically when the first element instance is created to
       * ensure that class finalization work has been completed.
       * May be called by users to eagerly perform class finalization work
       * prior to the creation of the first element instance.
       *
       * Class finalization work generally includes meta-programming such as
       * creating property accessors and any property effect metadata needed for
       * the features used.
       *
       * @public
       */
      static finalize() {
        if (!hasClassFinalized(this)) {
          finalizeClassAndSuper(this);
        }
      }

      /**
       * Returns the template that will be stamped into this element's shadow root.
       *
       * If a `static get is()` getter is defined, the default implementation
       * will return the first `<template>` in a `dom-module` whose `id`
       * matches this element's `is`.
       *
       * Users may override this getter to return an arbitrary template
       * (in which case the `is` getter is unnecessary). The template returned
       * may be either an `HTMLTemplateElement` or a string that will be
       * automatically parsed into a template.
       *
       * Note that when subclassing, if the super class overrode the default
       * implementation and the subclass would like to provide an alternate
       * template via a `dom-module`, it should override this getter and
       * return `Polymer.DomModule.import(this.is, 'template')`.
       *
       * If a subclass would like to modify the super class template, it should
       * clone it rather than modify it in place.  If the getter does expensive
       * work such as cloning/modifying a template, it should memoize the
       * template for maximum performance:
       *
       *   let memoizedTemplate;
       *   class MySubClass extends MySuperClass {
       *     static get template() {
       *       if (!memoizedTemplate) {
       *         memoizedTemplate = super.template.cloneNode(true);
       *         let subContent = document.createElement('div');
       *         subContent.textContent = 'This came from MySubClass';
       *         memoizedTemplate.content.appendChild(subContent);
       *       }
       *       return memoizedTemplate;
       *     }
       *   }
       *
       * @return {HTMLTemplateElement|string} Template to be stamped
       */
      static get template() {
        if (!this.hasOwnProperty(JSCompiler_renameProperty('_template', this))) {
          this._template = Polymer.DomModule && Polymer.DomModule.import(
            /** @type PolymerElementConstructor*/ (this).is, 'template') ||
            // note: implemented so a subclass can retrieve the super
            // template; call the super impl this way so that `this` points
            // to the superclass.
            Object.getPrototypeOf(/** @type PolymerElementConstructor*/ (this).prototype).constructor.template;
        }
        return this._template;
      }

      /**
       * Path matching the url from which the element was imported.
       * This path is used to resolve url's in template style cssText.
       * The `importPath` property is also set on element instances and can be
       * used to create bindings relative to the import path.
       * Defaults to the path matching the url containing a `dom-module` element
       * matching this element's static `is` property.
       * Note, this path should contain a trailing `/`.
       *
       * @return {string} The import path for this element class
       */
      static get importPath() {
        if (!this.hasOwnProperty(JSCompiler_renameProperty('_importPath', this))) {
            const module = Polymer.DomModule && Polymer.DomModule.import(/** @type PolymerElementConstructor */ (this).is);
            this._importPath = module ? module.assetpath : '' ||
            Object.getPrototypeOf(/** @type PolymerElementConstructor*/ (this).prototype).constructor.importPath;
        }
        return this._importPath;
      }

      constructor() {
        super();
        /** @type {HTMLTemplateElement} */
        this._template;
        /** @type {string} */
        this._importPath;
        /** @type {string} */
        this.rootPath;
        /** @type {string} */
        this.importPath;
        /** @type {StampedTemplate | HTMLElement | ShadowRoot} */
        this.root;
        /** @type {!Object<string, !Node>} */
        this.$;
      }

      /**
       * Overrides the default `Polymer.PropertyAccessors` to ensure class
       * metaprogramming related to property accessors and effects has
       * completed (calls `finalize`).
       *
       * It also initializes any property defaults provided via `value` in
       * `properties` metadata.
       *
       * @override
       * @suppress {invalidCasts}
       */
      _initializeProperties() {
        Polymer.telemetry.instanceCount++;
        this.constructor.finalize();
        const importPath = this.constructor.importPath;
        // note: finalize template when we have access to `localName` to
        // avoid dependence on `is` for polyfilling styling.
        if (this._template && !this._template.__polymerFinalized) {
          this._template.__polymerFinalized = true;
          const baseURI =
            importPath ? Polymer.ResolveUrl.resolveUrl(importPath) : '';
          finalizeTemplate(/** @type {!PolymerElement} */(this.__proto__), this._template, baseURI,
            /**@type {!HTMLElement}*/(this).localName);
        }
        super._initializeProperties();
        // set path defaults
        this.rootPath = Polymer.rootPath;
        this.importPath = importPath;
        // apply property defaults...
        let p$ = propertyDefaultsForClass(this.constructor);
        if (!p$) {
          return;
        }
        for (let p in p$) {
          let info = p$[p];
          // Don't set default value if there is already an own property, which
          // happens when a `properties` property with default but no effects had
          // a property set (e.g. bound) by its host before upgrade
          if (!this.hasOwnProperty(p)) {
            let value = typeof info.value == 'function' ?
              info.value.call(this) :
              info.value;
            // Set via `_setProperty` if there is an accessor, to enable
            // initializing readOnly property defaults
            if (this._hasAccessor(p)) {
              this._setPendingProperty(p, value, true);
            } else {
              this[p] = value;
            }
          }
        }
      }

      /**
       * Provides a default implementation of the standard Custom Elements
       * `connectedCallback`.
       *
       * The default implementation enables the property effects system and
       * flushes any pending properties, and updates shimmed CSS properties
       * when using the ShadyCSS scoping/custom properties polyfill.
       *
       * @suppress {invalidCasts}
       */
      connectedCallback() {
        if (window.ShadyCSS && this._template) {
          window.ShadyCSS.styleElement(/** @type {!HTMLElement} */(this));
        }
        this._enableProperties();
      }

      /**
       * Provides a default implementation of the standard Custom Elements
       * `disconnectedCallback`.
       */
      disconnectedCallback() {}

      /**
       * Stamps the element template.
       *
       * @override
       */
      ready() {
        if (this._template) {
          this.root = this._stampTemplate(this._template);
          this.$ = this.root.$;
        }
        super.ready();
      }

      /**
       * Implements `PropertyEffects`'s `_readyClients` call. Attaches
       * element dom by calling `_attachDom` with the dom stamped from the
       * element's template via `_stampTemplate`. Note that this allows
       * client dom to be attached to the element prior to any observers
       * running.
       *
       * @override
       */
      _readyClients() {
        if (this._template) {
          this.root = this._attachDom(/** @type {StampedTemplate} */(this.root));
        }
        // The super._readyClients here sets the clients initialized flag.
        // We must wait to do this until after client dom is created/attached
        // so that this flag can be checked to prevent notifications fired
        // during this process from being handled before clients are ready.
        super._readyClients();
      }


      /**
       * Attaches an element's stamped dom to itself. By default,
       * this method creates a `shadowRoot` and adds the dom to it.
       * However, this method may be overridden to allow an element
       * to put its dom in another location.
       *
       * @throws {Error}
       * @suppress {missingReturn}
       * @param {StampedTemplate} dom to attach to the element.
       * @return {ShadowRoot} node to which the dom has been attached.
       */
      _attachDom(dom) {
        if (this.attachShadow) {
          if (dom) {
            if (!this.shadowRoot) {
              this.attachShadow({mode: 'open'});
            }
            this.shadowRoot.appendChild(dom);
            return this.shadowRoot;
          }
          return null;
        } else {
          throw new Error('ShadowDOM not available. ' +
            // TODO(sorvell): move to compile-time conditional when supported
          'Polymer.Element can create dom as children instead of in ' +
          'ShadowDOM by setting `this.root = this;\` before \`ready\`.');
        }
      }

      /**
       * Provides a default implementation of the standard Custom Elements
       * `attributeChangedCallback`.
       *
       * By default, attributes declared in `properties` metadata are
       * deserialized using their `type` information to properties of the
       * same name.  "Dash-cased" attributes are deserialzed to "camelCase"
       * properties.
       *
       * @param {string} name Name of attribute.
       * @param {?string} old Old value of attribute.
       * @param {?string} value Current value of attribute.
       * @override
       */
      attributeChangedCallback(name, old, value) {
        if (old !== value) {
          let property = caseMap.dashToCamelCase(name);
          let type = propertiesForClass(this.constructor)[property].type;
          if (!this._hasReadOnlyEffect(property)) {
            this._attributeToProperty(name, value, type);
          }
        }
      }

      /**
       * When using the ShadyCSS scoping and custom property shim, causes all
       * shimmed styles in this element (and its subtree) to be updated
       * based on current custom property values.
       *
       * The optional parameter overrides inline custom property styles with an
       * object of properties where the keys are CSS properties, and the values
       * are strings.
       *
       * Example: `this.updateStyles({'--color': 'blue'})`
       *
       * These properties are retained unless a value of `null` is set.
       *
       * @param {Object=} properties Bag of custom property key/values to
       *   apply to this element.
       * @suppress {invalidCasts}
       */
      updateStyles(properties) {
        if (window.ShadyCSS) {
          window.ShadyCSS.styleSubtree(/** @type {!HTMLElement} */(this), properties);
        }
      }

      /**
       * Rewrites a given URL relative to a base URL. The base URL defaults to
       * the original location of the document containing the `dom-module` for
       * this element. This method will return the same URL before and after
       * bundling.
       *
       * @param {string} url URL to resolve.
       * @param {string=} base Optional base URL to resolve against, defaults
       * to the element's `importPath`
       * @return {string} Rewritten URL relative to base
       */
      resolveUrl(url, base) {
        if (!base && this.importPath) {
          base = Polymer.ResolveUrl.resolveUrl(this.importPath);
        }
        return Polymer.ResolveUrl.resolveUrl(url, base);
      }

      /**
       * Overrides `PropertyAccessors` to add map of dynamic functions on
       * template info, for consumption by `PropertyEffects` template binding
       * code. This map determines which method templates should have accessors
       * created for them.
       *
       * @override
       * @suppress {missingProperties} Interfaces in closure do not inherit statics, but classes do
       */
      static _parseTemplateContent(template, templateInfo, nodeInfo) {
        templateInfo.dynamicFns = templateInfo.dynamicFns || propertiesForClass(this);
        return super._parseTemplateContent(template, templateInfo, nodeInfo);
      }

    }

    return PolymerElement;
  });

  /**
   * Provides basic tracking of element definitions (registrations) and
   * instance counts.
   *
   * @namespace
   * @summary Provides basic tracking of element definitions (registrations) and
   * instance counts.
   */
  Polymer.telemetry = {
    /**
     * Total number of Polymer element instances created.
     * @type {number}
     */
    instanceCount: 0,
    /**
     * Array of Polymer element classes that have been finalized.
     * @type {Array<Polymer.Element>}
     */
    registrations: [],
    /**
     * @param {!PolymerElementConstructor} prototype Element prototype to log
     * @this {this}
     * @private
     */
    _regLog: function(prototype) {
      console.log('[' + prototype.is + ']: registered')
    },
    /**
     * Registers a class prototype for telemetry purposes.
     * @param {HTMLElement} prototype Element prototype to register
     * @this {this}
     * @protected
     */
    register: function(prototype) {
      this.registrations.push(prototype);
      Polymer.log && this._regLog(prototype);
    },
    /**
     * Logs all elements registered with an `is` to the console.
     * @public
     * @this {this}
     */
    dumpRegistrations: function() {
      this.registrations.forEach(this._regLog);
    }
  };

  /**
   * When using the ShadyCSS scoping and custom property shim, causes all
   * shimmed `styles` (via `custom-style`) in the document (and its subtree)
   * to be updated based on current custom property values.
   *
   * The optional parameter overrides inline custom property styles with an
   * object of properties where the keys are CSS properties, and the values
   * are strings.
   *
   * Example: `Polymer.updateStyles({'--color': 'blue'})`
   *
   * These properties are retained unless a value of `null` is set.
   *
   * @param {Object=} props Bag of custom property key/values to
   *   apply to the document.
   */
  Polymer.updateStyles = function(props) {
    if (window.ShadyCSS) {
      window.ShadyCSS.styleDocument(props);
    }
  };

})();
</script>