Fix issue where screen would eventually turn off if you switched apps and then came back

templates/new_workout.html

@@ -109,10 +109,11 @@
             let previousReadingTime = null;
 
             let screenLock;
-            navigator.wakeLock.request('screen')
-                .then(lock => {
-                    screenLock = lock;
-                });
+            document.addEventListener('visibilitychange', async () => {
+                if (screenLock !== null && document.visibilityState === 'visible') {
+                    screenLock = await navigator.wakeLock.request('screen');
+                }
+            });
 
             const integerNumber = (num) => parseInt(num);
             const decimalNumber = (num) => parseFloat(num.toFixed(1));