Add Navigation Arrow and simplify static page

public/js/distance.js

@@ -1,12 +1,33 @@
 (function (ns) {
   'use strict';
+
   const radians = value => value * Math.PI / 180;
+  const degrees = value => value * 180 / Math.PI;
+  const normalizeDegrees = value => (value % 360 + 360) % 360;
+
   ns.Distance = {
     meters(a, b) {
-      const dLat = radians(b.lat - a.lat); const dLon = radians(b.lon - a.lon);
-      const h = Math.sin(dLat / 2) ** 2 + Math.cos(radians(a.lat)) * Math.cos(radians(b.lat)) * Math.sin(dLon / 2) ** 2;
+      const dLat = radians(b.lat - a.lat);
+      const dLon = radians(b.lon - a.lon);
+      const h = Math.sin(dLat / 2) ** 2
+        + Math.cos(radians(a.lat)) * Math.cos(radians(b.lat)) * Math.sin(dLon / 2) ** 2;
       return 2 * 6371000 * Math.asin(Math.sqrt(h));
     },
-    format(meters) { return meters < 1000 ? `${Math.round(meters)} m` : `${(meters / 1000).toFixed(1)} km`; }
+
+    bearing(a, b) {
+      const lat1 = radians(a.lat);
+      const lat2 = radians(b.lat);
+      const dLon = radians(b.lon - a.lon);
+      const y = Math.sin(dLon) * Math.cos(lat2);
+      const x = Math.cos(lat1) * Math.sin(lat2)
+        - Math.sin(lat1) * Math.cos(lat2) * Math.cos(dLon);
+      return normalizeDegrees(degrees(Math.atan2(y, x)));
+    },
+
+    normalizeDegrees,
+
+    format(meters) {
+      return meters < 1000 ? `${Math.round(meters)} m` : `${(meters / 1000).toFixed(1)} km`;
+    }
   };
 }(window.Wegwichtel));