diff --git a/client.ts b/client.ts
index cf3c81d..1a37f37 100644
--- a/client.ts
+++ b/client.ts
@@ -31,6 +31,7 @@ let pendingEvts: Point[] = [];
 let isSpectator = false;  // is this client in spectator mode?
 let myId: number | null = null;
 let mySymbol: "x" | "o" | null = null;
+let animationId: number;
 let canvasMsg: string = "Offline...";
 
 function drawGridBackground(ctx: CanvasRenderingContext2D, origin: Point) {
@@ -43,7 +44,7 @@ function drawGridBackground(ctx: CanvasRenderingContext2D, origin: Point) {
     }
 
     for (let y = 1; y < 3; ++y) {
-        ctx.moveTo(origin.x + 0, origin.y + y * CELL_SIZE);
+        ctx.moveTo(origin.x, origin.y + y * CELL_SIZE);
         ctx.lineTo(origin.x + GRID_SIZE, origin.y + y * CELL_SIZE);
     }
 
@@ -53,13 +54,13 @@ function drawGridBackground(ctx: CanvasRenderingContext2D, origin: Point) {
 function resizeCanvas(ctx: CanvasRenderingContext2D) {
     ctx.canvas.width  = window.innerWidth;
     ctx.canvas.height = window.innerHeight;
-    ctx.clearRect(0, 0, ctx.canvas.height, ctx. canvas.width);
+    ctx.clearRect(0, 0, ctx.canvas.width, ctx. canvas.height);
 }
 
 function coordToGridIndex(origin: Point, clientPos: Point): [number, number] | undefined {
     // Coord relative to origin of the grid (origin)
     const pt = { x: clientPos.x - origin.x, y: clientPos.y - origin.y };
-    const gridIndex: [number, number] = [Math.floor(3 * pt.x / GRID_SIZE), Math.floor(3 * pt.y / GRID_SIZE)];
+    const gridIndex: [number, number] = [Math.floor(pt.x / CELL_SIZE), Math.floor(pt.y / CELL_SIZE)];
     if (gridIndex[0] >= 0 && gridIndex[0] <= 2 && gridIndex[1] >= 0 && gridIndex[1] <= 2) {
         return gridIndex;
     }
@@ -169,7 +170,7 @@ function update(ctx: CanvasRenderingContext2D, time: number, ws: WebSocket) {
     handlePendingEvts(ws, gridOrigin);
     updateGridState(ctx, time, gridOrigin);
 
-    window.requestAnimationFrame(t => update(ctx, t, ws));
+    animationId = window.requestAnimationFrame(t => update(ctx, t, ws));
 }
 
 function init() {
@@ -190,12 +191,26 @@ function init() {
     });
 
     // websocket stuff
-    ws.onopen = (e) => {
+    ws.onopen = () => {
         console.log("connected to websocket server");
     };
 
+    ws.onerror = () => {
+        canvasMsg = "Connection error!";
+    };
+
+    ws.onclose = () => {
+        canvasMsg = "Disconnected";
+    };
+
     ws.onmessage = (evt) => {
-        const msg: Message = JSON.parse(evt.data);
+        let msg: Message;
+        try {
+            msg = JSON.parse(evt.data);
+        } catch {
+            console.debug("received non-JSON message, ignoring");
+            return;
+        }
         console.log(msg);
         switch (msg.kind) {
             case "hello": {
@@ -260,6 +275,7 @@ function init() {
 
     window.addEventListener('resize', () => resizeCanvas(ctx));
     window.requestAnimationFrame(t => update(ctx, t, ws));
+    window.addEventListener('beforeunload', () => cancelAnimationFrame(animationId));
 }
 
 init();
diff --git a/server.ts b/server.ts
index cc38098..e1758f9 100644
--- a/server.ts
+++ b/server.ts
@@ -1,14 +1,15 @@
 import type { Message, Update, Hello, EndGame, Symbol, SymbolWithHue } from "common.js"
 import { WebSocket, WebSocketServer, MessageEvent } from "ws";
 
-const port = 1234
-const wss = new WebSocketServer({ port });
+const PORT = 1234;
+const GRID_SIZE = 3;
+const wss = new WebSocketServer({ port: PORT });
 
 let grid = [0, 0, 0, 0, 0, 0, 0, 0, 0];
 let hues = [0, 0, 0, 0, 0, 0, 0, 0, 0];
 let endGame = false;
 
-console.log(`waiting for connection on ws://localhost:${port}`);
+console.log(`waiting for connection on ws://localhost:${PORT}`);
 
 interface Client {
     id: number,
@@ -36,7 +37,12 @@ wss.on("connection", (ws, req) => {
             if (playerId === 0) {
                 spectateData.push(undefined);
             } else {
-                const sym = clients.find(c => c.id === playerId)!.symbol;
+                const client = clients.find(c => c.id === playerId);
+                if (!client) {
+                    spectateData.push(undefined);
+                    continue;
+                }
+                const sym = client.symbol;
                 const hue = hues[i];
                 spectateData.push({ symbol: sym, hue: hue });
             }
@@ -55,15 +61,25 @@ wss.on("connection", (ws, req) => {
     const helloMsg: Message = {
         kind: "hello",
         data: { id, symbol } as Hello
-    }
+    };
     clients.push({id, ws, symbol});
     ws.send(JSON.stringify(helloMsg));
     const addr = req.headers["x-forwarded-for"] || req.socket.remoteAddress;
     console.log(`player #${id} connected with address ${addr}. total clients ${clients.length}`);
 
     ws.addEventListener("message", (event: MessageEvent) => {
-        const message = JSON.parse(event.data as string);
+        let message;
+        try {
+            message = JSON.parse(event.data as string);
+        } catch {
+            console.warn("received non-JSON message, ignoring");
+            return;
+        }
         const {x, y} = message;
+        if (x < 0 || x >= GRID_SIZE || y < 0 || y >= GRID_SIZE) {
+            console.warn("received invalid move, ignoring");
+            return;
+        }
         const hue = Math.floor(Math.random() * 361); // hue is a value in degrees
         const player = clients.find(x => x.ws === ws);
         if (!player) throw new Error("player not found");
@@ -93,12 +109,12 @@ wss.on("connection", (ws, req) => {
             }
         }
 
-        if (clients.length < 2 || player.id != currentPlayer?.id || endGame) {
+        if (clients.length < 2 || player.id !== currentPlayer?.id || endGame) {
             return;
         }
 
-        if (grid[y*3+x] === 0) {
-            grid[y*3+x] = player.id;
+        if (grid[y * GRID_SIZE + x] === 0) {
+            grid[y * GRID_SIZE + x] = player.id;
             hues[y*3+x] = hue;
             const msg = JSON.stringify({
                 kind: "update",
@@ -151,7 +167,7 @@ wss.on("connection", (ws, req) => {
         }
     });
 
-    ws.on("close", (code: number) => {
+    ws.on("close", () => {
         spectators = spectators.filter(s => s.readyState !== WebSocket.CLOSED);
         const isClientDisconnect = clients.some(c => c.ws === ws);
         if (isClientDisconnect) {