Adding code property to SyntheticKeyboardEvent with test

packages/react-dom/src/events/SyntheticKeyboardEvent.js

@@ -54,6 +54,23 @@ var KeyboardEventInterface = {
     }
     return 0;
   },
+  code: function(event) {
+    // `code` represents a physical key on the keyboard, as opposed to the character
+    // generated by pressing the key.
+
+    // It returns a value not altered by keyboard layout
+    // or the state of the modifier keys.
+
+    // Assuming the input doesn't come from a physical keyboard, but instead from a virtual
+    // keyboard or accessibility device, it will be returned a value set by the browser to match
+    // as closely as possible to what would happen with a physical keyboard, to maximize
+    // compatibility between physical and virtual input devices.
+    if (event.type === 'keydown' || event.type === 'keyup') {
+      return event.code;
+    }
+
+    return 0;
+  },
   which: function(event) {
     // `which` is an alias for either `keyCode` or `charCode` depending on the
     // type of the event.

packages/react-dom/src/events/__tests__/SyntheticKeyboardEvent-test.js

@@ -63,6 +63,22 @@ describe('SyntheticKeyboardEvent', () => {
       });
     });
 
+    describe('code', () => {
+      describe('when event is `keydown` or `keyup`', () => {
+        it('returns a passed code', () => {
+          var keyboardEvent = createEvent({type: 'keyup', code: 'ArrowDown'});
+          expect(keyboardEvent.code).toBe('ArrowDown');
+        });
+      });
+
+      describe('when event is `keypress`', () => {
+        it('returns 0', () => {
+          var keyboardEvent = createEvent({type: 'keypress', charCode: 40});
+          expect(keyboardEvent.code).toBe(0);
+        });
+      });
+    });
+
     describe('which', () => {
       describe('when event is `keypress`', () => {
         it('returns whatever getEventCharCode returns', () => {