Initial implementation of overlay functionality

src/fetchData.js

@@ -6,7 +6,7 @@ export default async function fetchData(currentRegionSelection, currentTimeSelec
     const resp = await fetch(urlBuilder(currentRegionSelection, currentTimeSelection, currentAggregateSelection));
     const respData = await resp.json();
     for (let i = 0, l = respData.length; i < l; i++) {
-        let datum = new Datum(Date.parse(respData[i][0]), respData[i][1]);
+        const datum = new Datum(new Date(respData[i][0]), respData[i][1]);
         data.push(datum);
     }
     return data;