Refactored App component from index.tsx

src/app.tsx

@@ -0,0 +1,40 @@
+import * as React from 'react';
+import {ChartView} from './chart_view';
+import {Route, RouteComponentProps, Switch} from 'react-router-dom';
+import {Intro} from './intro';
+import {TopBar} from './top_bar';
+
+export class App extends React.Component<{}, {}> {
+  chartViewRef?: ChartView;
+
+  render() {
+    return (
+      <div className="root">
+        <Route
+          component={(props: RouteComponentProps) => (
+            <TopBar
+              {...props}
+              onPrint={() => this.chartViewRef && this.chartViewRef.print()}
+              onDownloadSvg={() =>
+                this.chartViewRef && this.chartViewRef.downloadSvg()
+              }
+              onDownloadPng={() =>
+                this.chartViewRef && this.chartViewRef.downloadPng()
+              }
+            />
+          )}
+        />
+        <Switch>
+          <Route exact path="/" component={Intro} />
+          <Route
+            exact
+            path="/view"
+            component={(props: RouteComponentProps) => (
+              <ChartView {...props} ref={(ref) => (this.chartViewRef = ref!)} />
+            )}
+          />
+        </Switch>
+      </div>
+    );
+  }
+}