properties-mixin.js

/**
@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
*/
import '../utils/boot.js';

import { dedupingMixin } from '../utils/mixin.js';
import { register, incrementInstanceCount } from '../utils/telemetry.js';
import { PropertiesChanged } from './properties-changed.js';

/**
 * Creates a copy of `props` with each property normalized such that
 * upgraded it is an object with at least a type property { type: Type}.
 *
 * @param {Object} props Properties to normalize
 * @return {Object} Copy of input `props` with normalized properties that
 * are in the form {type: Type}
 * @private
 */
function normalizeProperties(props) {
  const output = {};
  for (let p in props) {
    const o = props[p];
    output[p] = (typeof o === 'function') ? {type: o} : o;
  }
  return output;
}

/**
 * Mixin that provides a minimal starting point to using the PropertiesChanged
 * mixin by providing a mechanism to declare properties in a static
 * getter (e.g. static get properties() { return { foo: String } }). Changes
 * are reported via the `_propertiesChanged` method.
 *
 * This mixin provides no specific support for rendering. Users are expected
 * to create a ShadowRoot and put content into it and update it in whatever
 * way makes sense. This can be done in reaction to properties changing by
 * implementing `_propertiesChanged`.
 *
 * @mixinFunction
 * @polymer
 * @appliesMixin PropertiesChanged
 * @summary Mixin that provides a minimal starting point for using
 * the PropertiesChanged mixin by providing a declarative `properties` object.
 */
export const PropertiesMixin = dedupingMixin(superClass => {

 /**
  * @constructor
  * @implements {Polymer_PropertiesChanged}
  * @private
  */
 const base = PropertiesChanged(superClass);

 /**
  * Returns the super class constructor for the given class, if it is an
  * instance of the PropertiesMixin.
  *
  * @param {!PropertiesMixinConstructor} constructor PropertiesMixin constructor
  * @return {?PropertiesMixinConstructor} Super class constructor
  */
 function superPropertiesClass(constructor) {
   const superCtor = Object.getPrototypeOf(constructor);

   // Note, the `PropertiesMixin` class below only refers to the class
   // generated by this call to the mixin; the instanceof test only works
   // because the mixin is deduped and guaranteed only to apply once, hence
   // all constructors in a proto chain will see the same `PropertiesMixin`
   return (superCtor.prototype instanceof PropertiesMixin) ?
     /** @type {!PropertiesMixinConstructor} */ (superCtor) : null;
 }

 /**
  * Returns a memoized version of the `properties` object for the
  * given class. Properties not in object format are converted to at
  * least {type}.
  *
  * @param {PropertiesMixinConstructor} constructor PropertiesMixin constructor
  * @return {Object} Memoized properties object
  */
 function ownProperties(constructor) {
   if (!constructor.hasOwnProperty(JSCompiler_renameProperty('__ownProperties', constructor))) {
     let props = null;

     if (constructor.hasOwnProperty(JSCompiler_renameProperty('properties', constructor))) {
       const properties = constructor.properties;

       if (properties) {
        props = normalizeProperties(properties);
       }
     }

     constructor.__ownProperties = props;
   }
   return constructor.__ownProperties;
 }

 /**
  * @polymer
  * @mixinClass
  * @extends {base}
  * @implements {Polymer_PropertiesMixin}
  * @unrestricted
  */
 class PropertiesMixin extends base {

   /**
    * Implements standard custom elements getter to observes the attributes
    * listed in `properties`.
    * @suppress {missingProperties} Interfaces in closure do not inherit statics, but classes do
    * @nocollapse
    */
   static get observedAttributes() {
     if (!this.hasOwnProperty('__observedAttributes')) {
       register(this.prototype);
       const props = this._properties;
       this.__observedAttributes = props ? Object.keys(props).map(p => this.attributeNameForProperty(p)) : [];
     }
     return this.__observedAttributes;
   }

   /**
    * Finalizes an element definition, including ensuring any super classes
    * are also finalized. This includes ensuring property
    * accessors exist on the element prototype. This method calls
    * `_finalizeClass` to finalize each constructor in the prototype chain.
    * @return {void}
    * @nocollapse
    */
   static finalize() {
     if (!this.hasOwnProperty(JSCompiler_renameProperty('__finalized', this))) {
       const superCtor = superPropertiesClass(/** @type {!PropertiesMixinConstructor} */(this));
       if (superCtor) {
         superCtor.finalize();
       }
       this.__finalized = true;
       this._finalizeClass();
     }
   }

   /**
    * Finalize an element class. This includes ensuring property
    * accessors exist on the element prototype. This method is called by
    * `finalize` and finalizes the class constructor.
    *
    * @protected
    * @nocollapse
    */
   static _finalizeClass() {
     const props = ownProperties(/** @type {!PropertiesMixinConstructor} */(this));
     if (props) {
       this.createProperties(props);
     }
   }

   /**
    * Returns a memoized version of all properties, including those inherited
    * from super classes. Properties not in object format are converted to
    * at least {type}.
    *
    * @return {Object} Object containing properties for this class
    * @protected
    * @nocollapse
    */
   static get _properties() {
     if (!this.hasOwnProperty(
       JSCompiler_renameProperty('__properties', this))) {
       const superCtor = superPropertiesClass(/** @type {!PropertiesMixinConstructor} */(this));
       this.__properties = Object.assign({},
         superCtor && superCtor._properties,
         ownProperties(/** @type {PropertiesMixinConstructor} */(this)));
     }
     return this.__properties;
   }

   /**
    * Overrides `PropertiesChanged` method to return type specified in the
    * static `properties` object for the given property.
    * @param {string} name Name of property
    * @return {*} Type to which to deserialize attribute
    *
    * @protected
    * @nocollapse
    */
   static typeForProperty(name) {
     const info = this._properties[name];
     return info && info.type;
   }

   /**
    * Overrides `PropertiesChanged` method and adds a call to
    * `finalize` which lazily configures the element's property accessors.
    * @override
    * @return {void}
    */
   _initializeProperties() {
     incrementInstanceCount();
     this.constructor.finalize();
     super._initializeProperties();
   }

   /**
    * Called when the element is added to a document.
    * Calls `_enableProperties` to turn on property system from
    * `PropertiesChanged`.
    * @suppress {missingProperties} Super may or may not implement the callback
    * @return {void}
    * @override
    */
   connectedCallback() {
     if (super.connectedCallback) {
       super.connectedCallback();
     }
     this._enableProperties();
   }

   /**
    * Called when the element is removed from a document
    * @suppress {missingProperties} Super may or may not implement the callback
    * @return {void}
    * @override
    */
   disconnectedCallback() {
     if (super.disconnectedCallback) {
       super.disconnectedCallback();
     }
   }

 }

 return PropertiesMixin;

});