Ensure _.defaults assigns properties that shadow those on Object.prototype.

lodash.js

@@ -587,18 +587,6 @@
     return false;
   }
 
-  /**
-   * Used by `_.defaults` to customize its `_.assignIn` use.
-   *
-   * @private
-   * @param {*} objValue The destination object property value.
-   * @param {*} srcValue The source object property value.
-   * @returns {*} Returns the value to assign to the destination object.
-   */
-  function assignInDefaults(objValue, srcValue) {
-    return objValue === undefined ? srcValue : objValue;
-  }
-
   /**
    * Assigns `value` to `key` of `object` if the existing value is not equivalent
    * using [`SameValueZero`](http://ecma-international.org/ecma-262/6.0/#sec-samevaluezero)
@@ -2137,6 +2125,21 @@
 
     /*------------------------------------------------------------------------*/
 
+    /**
+     * Used by `_.defaults` to customize its `_.assignIn` use.
+     *
+     * @private
+     * @param {*} objValue The destination value.
+     * @param {*} srcValue The source value.
+     * @param {string} key The key of the property to assign.
+     * @returns {*} Returns the value to assign.
+     */
+    function assignInDefaults(objValue, srcValue, key) {
+      return (objValue === undefined || objValue === objectProto[key])
+        ? srcValue
+        : objValue;
+    }
+
     /**
      * The base implementation of `_.assign` without support for multiple sources
      * or `customizer` functions.
@@ -4853,9 +4856,9 @@
      * Used by `_.defaultsDeep` to customize its `_.merge` use.
      *
      * @private
-     * @param {*} objValue The destination object property value.
-     * @param {*} srcValue The source object property value.
-     * @returns {*} Returns the value to assign to the destination object.
+     * @param {*} objValue The destination value.
+     * @param {*} srcValue The source value.
+     * @returns {*} Returns the value to assign.
      */
     function mergeDefaults(objValue, srcValue, key, object, source, stack) {
       if (isObject(objValue) && isObject(srcValue)) {

test/test.js

@@ -3626,6 +3626,13 @@
       var actual = _.defaults({ 'a': undefined }, { 'a': 1 });
       assert.strictEqual(actual.a, 1);
     });
+
+    QUnit.test('should assign properties that shadow those on `Object.prototype`', function(assert) {
+      assert.expect(1);
+
+      var actual = _.defaults({}, { 'constructor': 1 });
+      assert.strictEqual(actual.constructor, 1);
+    });
   }());
 
   /*--------------------------------------------------------------------------*/