display NaN values as undefined

Summary: NaN values now display a placeholder saying undefined.

Reviewed By: emilsjolander

Differential Revision: D7009509

fbshipit-source-id: a3af360cc5c9d93e95a9e10368270f053a9b2c08

website/src/components/Playground/EditValue.js

@@ -35,6 +35,8 @@ export default (props: Props<*>) => {
         type="text"
         {...props}
         onChange={e => props.onChange(props.property, e.target.value)}
+        placeholder="undefined"
+        value={Number.isNaN(props.value) ? '' : props.value}
       />
     );
   }

website/src/components/Playground/index.js

@@ -149,11 +149,7 @@ export default class Playground extends Component<Props, State> {
       const updatedChildren = layoutDefinition
         .getIn(path)
         .push(LayoutRecord({width: 100, height: 100}));
-      this.modifyAtPath(
+      this.modifyAtPath(path, updatedChildren);
-        path,
-        updatedChildren,
-        selectedNodePath.concat(updatedChildren.size - 1),
-      );
     }
   };