fix(common): Re-fix implementation of 'pick' using for .. in

Previous change to hasOwnProperty (released in 5.0.2) was not correct.

Closes #53

src/common/common.ts

@@ -225,7 +225,7 @@ export const mergeR = (memo: Obj, item: Obj) => extend(memo, item);
 export function ancestors(first: StateObject, second: StateObject) {
   let path: StateObject[] = [];
 
-  for (var n in first.path) {
+  for (let n in first.path) {
     if (first.path[n] !== second.path[n]) break;
     path.push(first.path[n]);
   }
@@ -244,9 +244,13 @@ export function ancestors(first: StateObject, second: StateObject) {
  * @param propNames an Array of strings, which are the whitelisted property names
  */
 export function pick(obj: Obj, propNames: string[]): Obj {
-  let copy = {};
-  propNames.forEach(prop => { if (obj.hasOwnProperty(prop)) copy[prop] = obj[prop] });
-  return copy;
+  let objCopy = {};
+  for (let prop in obj) {
+    if (propNames.indexOf(prop) !== -1) {
+      objCopy[prop] = obj[prop];
+    }
+  }
+  return objCopy;
 }
 
 /**

test/commonSpec.ts

@@ -1,6 +1,7 @@
 import {
     defaults, filter, is, eq, not, pattern, val, isInjectable
 } from "../src/index";
+import { pick } from '../src/common/common';
 
 describe('common', function() {
   describe('filter', function() {
@@ -112,4 +113,17 @@ describe('common', function() {
       expect(isInjectable(fn)).toBeTruthy();
     });
   });
+
+  describe('pick', () => {
+    it('should pick inherited properties', () => {
+      let parent = { foo: 'foo', bar: 'bar' };
+      let child = Object.create(parent);
+      expect(pick(child, ['foo'])).toEqual({ foo: 'foo' });
+    });
+
+    it('should not pick missing properties', () => {
+      let obj = { foo: 'foo', bar: 'bar' };
+      expect(pick(obj, ['baz'])).toEqual({ });
+    });
+  });
 });