Fix sessionStorage bug #10

Fixed bug with JSON syntax error on reloading a page with sessionstorage

frontend/src/Components/ArtPage.tsx

@@ -35,8 +35,9 @@ class ArtPage extends React.Component<props, state> {
         const pageId = this.props.pageId.toString();
         const choices = sessionStorage.getItem(pageId); // Previously stored options. Saved as string
         if (choices != null) { // We have stored something previously
-            const choicesObject = JSON.parse(choices); // Convert string to object
-            sessionStorage.setItem(pageId, {...choicesObject, [label]: choice}); // Update choices
+            const choicesObject: object = JSON.parse(choices); // Convert string to object
+            let choicesObjectStringified : string = JSON.stringify({...choicesObject, [label]: choice});
+            sessionStorage.setItem(pageId, choicesObjectStringified); // Update choices
         } else
             sessionStorage.setItem(pageId, JSON.stringify({...this.state.options, [label]: choice}));
     };