Add 'size' getter to Y.Map

src/types/YMap.js

@@ -115,6 +115,15 @@ export class YMap extends AbstractType {
     return map
   }
 
+  /**
+   * Returns the size of the YMap (count of key/value pairs)
+   *
+   * @return {number}
+   */
+  get size () {
+    return [...createMapIterator(this._map)].length
+  }
+
   /**
    * Returns the keys for each element in the YMap Type.
    *
@@ -143,7 +152,7 @@ export class YMap extends AbstractType {
   }
 
   /**
-   * Executes a provided function on once on overy key-value pair.
+   * Executes a provided function on once on every key-value pair.
    *
    * @param {function(T,string,YMap<T>):void} f A function to execute on every element of this YArray.
    */