never setState after component is unmounted

Example/examples/G.js

@@ -23,12 +23,18 @@ class GExample extends Component{
 
     componentDidMount = () => {
         setTimeout(() => {
+            if (!this._unmounted) {
                 this.setState({
                     fill: '#856'
                 });
+            }
         }, 2000);
     };
 
+    componentWillUnmount = () => {
+        this._unmounted = true;
+    };
+
     render() {
         return <Svg
             height="100"