Move function out of closure. Add comments.

lib/mixins/properties-mixin.html

@@ -16,6 +16,24 @@
 (function() {
   'use strict';
 
+  /**
+    * Mixes `moreProps` into `props` but upgrades shorthand type
+    * syntax to { 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
@@ -43,44 +61,29 @@
      */
     const base = Polymer.PropertiesChanged(superClass);
 
-    /**
-     * Mixes `moreProps` into `props` but upgrades shorthand type
-     * syntax to { 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;
-    }
-
     /**
      * 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
+     * @param {!PropertiesMixin} constructor PropertiesMixin constructor
+     * @return {PropertiesMixin} Super class constructor
      */
     function superPropertiesClass(constructor) {
       const superCtor = Object.getPrototypeOf(constructor);
-      if (superCtor.prototype instanceof PropertiesMixin) {
-        return superCtor;
-      }
+      // 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 {PropertiesMixin} */ (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
+     * @param {PropertiesMixin} constructor PropertiesMixin constructor
      * @return {Object} Memoized properties object
      */
     function ownProperties(constructor) {
@@ -189,14 +192,12 @@
        * `PropertiesChanged`.
        */
       connectedCallback() {
+        if (super.connectedCallback) {
+          super.connectedCallback();
+        }
         this._enableProperties();
       }
 
-      /**
-       * Called when the element is removed from a document
-       */
-      disconnectedCallback() {}
-
     }
 
     return PropertiesMixin;