1  let startTime;
 2  let markers = [];
 3  
 4  module.exports = {
 5    setStartTime() {
 6      if (!startTime) {
 7        startTime = Date.now();
 8      }
 9    },
10    addMarker(label, dateTime) {
11      if (!startTime) {
12        return;
13      }
14  
15      dateTime = dateTime || Date.now();
16      markers.push({ label, time: dateTime - startTime });
17    },
18    importData(data) {
19      startTime = data.startTime;
20      markers = data.markers;
21    },
22    exportData() {
23      if (!startTime) {
24        return undefined;
25      }
26  
27      return { startTime, markers };
28    },
29    deleteData() {
30      startTime = undefined;
31      markers = [];
32    }
33  };