smoother progress bar, prevent browser from interfering with escape key

dlibrary/static/viewer.js

@@ -1,3 +1,5 @@
+const PROGRESS_UPDATE_INTERVAL = 50;
+
 document.addEventListener('DOMContentLoaded', () => {
     const pages = Array.from(document.querySelectorAll('img.viewer-image'));
     let currentPage = parseInt(localStorage.getItem(`${WORK_ID}-currentPage`)) || 0;
@@ -16,13 +18,13 @@ document.addEventListener('DOMContentLoaded', () => {
                 if (paused) {
                     return;
                 }
-                elapsed += 100;
+                elapsed += PROGRESS_UPDATE_INTERVAL;
                 if (elapsed >= duration*1000) {
                     changePage(currentPage + 1);
                 }
                 updateBar();
             },
-            100
+            PROGRESS_UPDATE_INTERVAL,
         );
     }
 
@@ -119,15 +121,19 @@ document.addEventListener('DOMContentLoaded', () => {
 
         switch (event.key) {
         case "ArrowLeft":
+            event.preventDefault();
             left();
             break;
         case "ArrowRight":
+            event.preventDefault();
             right();
             break;
         case " ":
+            event.preventDefault();
             changeDuration(duration, !paused);
             break;
         case "ArrowUp":
+            event.preventDefault();
             if (2 <= duration && duration <= 10) {
                 changeDuration(duration - 1, false);
             } else if (10 < duration && duration <= 20) {
@@ -137,6 +143,7 @@ document.addEventListener('DOMContentLoaded', () => {
             }
             break;
         case "ArrowDown":
+            event.preventDefault();
             if (duration < 10) {
                 changeDuration(duration + 1, false);
             } else if (10 <= duration && duration < 20) {
@@ -146,9 +153,11 @@ document.addEventListener('DOMContentLoaded', () => {
             }
             break;
         case "Enter":
+            event.preventDefault();
             restart();
             break;
         case "Escape":
+            event.preventDefault();
             exitToWork();
             break;
         }