Stop simulation when page is hidden

index.mjs

@@ -45,6 +45,7 @@ for (let i = 0; i < 300; ++i)
     });
 }
 
+let paused = false;
 let lastTime = null;
 
 const loop = time =>
@@ -60,7 +61,34 @@ const loop = time =>
     boids.update(activeBoids, params, delta);
     draw.fill(activeBoids, params, boidsCtx, width, height, center);
 
+    if (!paused)
+    {
+        requestAnimationFrame(loop);
+    }
+};
+
+const start = () =>
+{
+    lastTime = null;
+    paused = false;
     requestAnimationFrame(loop);
 };
 
-requestAnimationFrame(loop);
+const pause = () =>
+{
+    paused = true;
+};
+
+document.onvisibilitychange = () =>
+{
+    if (document.visibilityState === 'visible')
+    {
+        start();
+    }
+    else
+    {
+        pause();
+    }
+};
+
+start();