Implement P2P polling app with Yjs and WebRTC

Uses Yjs CRDTs for conflict-free shared state and y-webrtc for peer-to-peer data exchange. Users can add poll options and vote/unvote, with all changes syncing in real-time across connected peers. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
2026-03-15 04:32:06 +01:00
10 changed files with 1669 additions and 611 deletions
--- a/.gitignore
+++ b/.gitignore
@@ -1 +0,0 @@
 node_modules/
--- a/README.md
+++ b/README.md
@@ -1,28 +1 @@
 # P2P Poll App
 ## Install npm packages
 ```
 npm init -y
 npm install
 ```
 Note: the frontend obtains the packages `yjs` and `y-websocket` dynamically.
 ## Run backend
 ```
 node backend.js
 ```
 ### Note on Yjs suggestion
 Note that the following server setup is suggested in the Yjs docs (https://docs.yjs.dev/ecosystem/connection-provider/y-websocket):
 ```
 npm install y-websocket-server
 HOST=localhost PORT=1000 npx y-websocket
 ```
 However, across a range of npm versions, this does not work.
 Nevertheless, the essential code from the `y-websocket-server` package is used here as provided in `utils.js`.
 ## Run frontend
 Open "frontend.html" in browser.
--- a/backend.js
+++ b/backend.js
@@ -1,31 +0,0 @@
 import { WebSocketServer } from 'ws';
 import { setupWSConnection } from './utils.js'
 // Create a WebSocket server
 const WS_PORT = 8080;
 const wss = new WebSocketServer({ port: WS_PORT });
 console.log('WebSocket server is running on ws://localhost:' + String(WS_PORT));
 // Connection event handler
 wss.on('connection', setupWSConnection);
 /*
 wss.on('connection', (ws) => {
  console.log('Client connected');
  // Message event handler
  ws.on('message', (message) => {
    let msg_str = String(message);
    console.log("Received: " + msg_str);
    // If this is a text or state message (no Yjs logic) - echo the message back to the client
    if (msg_str.startsWith("TEXT_MESSAGE") | msg_str.startsWith("STATE_MESSAGE")) {
      ws.send(msg_str);
    }
  });
  // Close event handler
  ws.on('close', () => {
    console.log('Client disconnected');
  });
 });*/
--- a/frontend.html
+++ b/frontend.html
@@ -1,196 +0,0 @@
 <!DOCTYPE html>
 <html>
 <head>
  <title>Poll Client</title>
  <style>
    body {
      font-family: Arial, sans-serif;
      max-width: 600px;
      margin: 0 auto;
      padding: 20px;
    }
    #messages {
      height: 300px;
      border: 1px solid #ccc;
      overflow-y: auto;
      padding: 10px;
      margin-bottom: 10px;
    }
    .message { margin: 5px 0; }
  </style>
 </head>
 <body>
  <h1>Poll Client</h1>
  <div id="status">Connecting to server...</div>
  <div id="status2">Connecting to server...</div>
  <div id="messages"></div>
  <div>
    <input type="text" id="messageInput" placeholder="Type your message">
    <!--button onclick="sendMessage()">Send</button-->
    <button id="sendBtn">Send</button>
    <input id="optionInput" placeholder="Add option">
    <button id="addBtn">Add</button>
    <ul id="options"></ul>
  </div>
  <script type="module">
    import * as Y from "https://esm.sh/yjs"
    import { WebsocketProvider } from "https://esm.sh/y-websocket"
    const WS_PORT = 8080;
    const ydoc = new Y.Doc();
    const status = document.getElementById('status');
    const status2 = document.getElementById('status2');
    const messages = document.getElementById('messages');
    const messageInput = document.getElementById('messageInput');
    // Connect to the backend (WebSocket server) via Yjs WebsocketProvider
    const wsp = new WebsocketProvider(
      'ws://localhost:' + String(WS_PORT), 'poll-room',
      ydoc
    )
    wsp.on('status', event => {
      //console.log("event.status =", event.status)
      if (event.status == "connected") {
        status.textContent = 'Yjs connected to WebSocket server';
        status.style.color = 'green';
      }
      else {
        status.textContent = 'Yjs disonnected from WebSocket server';
        status.style.color = 'red';
      }
    })
    wsp.onopen = () => {
      console.log('connected to y-websocket server');
    };
    ydoc.on('update', () => {
      console.log('Yjs document updated locally');
    });
    wsp.on('sync', isSynced => {
      console.log("isSynced =", isSynced)
    })
    // Connect to the backend (WebSocket server) via common WebSocket (only for informative messages)
    const ws = new WebSocket('ws://localhost:' + String(WS_PORT));
    ws.onopen = () => {
      status2.textContent = 'WebSocket client connected to WebSocket server';
      status2.style.color = 'green';
    };
    ws.onmessage = (event) => {
      const message = document.createElement('div');
      message.className = 'message';
      message.textContent = event.data;
      messages.appendChild(message);
      messages.scrollTop = messages.scrollHeight;
    };
    ws.onerror = (error) => {
      status2.textContent = 'Error: ' + error.message;
      status2.style.color = 'red';
    };
    ws.onclose = () => {
      status2.textContent = 'WebSocket client disconnected from WebSocket server';
      status2.style.color = 'red';
    };
    // Function to send a message
    function sendMessage(command, payload) {
        let message = "";
        if (command === "TEXT_MESSAGE") {
            message = command + ":" + messageInput.value.trim();
            messageInput.value = "";
        }
        else if (command.startsWith("STATE_MESSAGE--")) {
            message = command + ":" + payload;
        }
        else {
            console.log("Error: unknown command '" + command + "'")
        }
        if (message) {
            /* To make compatible with y-websocket-server API:
            const encoder = encoding.createEncoder()
            encoding.writeVarUint(encoder, messageTextMessage)
            syncProtocol.writeUpdate(encoder, update)
            enc_message = encoding.toUint8Array(encoder)*/
            ws.send(message);
        }
    }
     // Send message on button click
    document.getElementById("sendBtn").onclick = () => {
        sendMessage("TEXT_MESSAGE", "");
    };
    // Send message on Enter key
    messageInput.addEventListener('keypress', (e) => {
      if (e.key === 'Enter') {
        sendMessage("TEXT_MESSAGE", "");
      }
    });
    // Actual poll logic
    const optionsMap = ydoc.getMap("options");
    const optionsList = document.getElementById("options");
    const input = document.getElementById("optionInput");
    function render() {
        optionsList.innerHTML = ""
        optionsMap.forEach((vote, name) => {
            // List element for this option
            const li = document.createElement("li")
            // Label for this option
            const label = document.createElement("span")
            label.textContent = name + " — " + vote + " "
            // "Vote"/"Unvote" button
            const voteBtn = document.createElement("button")
            if (vote == false) {
                voteBtn.textContent = "Vote"
            }
            else {
                voteBtn.textContent = "Unvote"
            }
            voteBtn.onclick = () => {
                vote = !vote;
                optionsMap.set(name, vote);
                sendMessage("STATE_MESSAGE--" + (vote ? "VOTE" : "UNVOTE"), name);
            }
            // "Remove" button
            const removeBtn = document.createElement("button")
            removeBtn.textContent = "Remove"
            removeBtn.onclick = () => {
                optionsMap.delete(name);
                sendMessage("STATE_MESSAGE--REMOVE", name);
            }
            li.appendChild(label)
            li.appendChild(voteBtn)
            li.appendChild(removeBtn)
            optionsList.appendChild(li)
        })
    };
    document.getElementById("addBtn").onclick = () => {
        const name = input.value.trim()
        if (!name) return
        if (!optionsMap.has(name)) {
            optionsMap.set(name, false);
            sendMessage("STATE_MESSAGE--ADD_OPTION", name);
        }
        input.value = ""
    };
    optionsMap.observe(render);
    render();
  </script>
 </body>
 </html>
--- a/index.html
+++ b/index.html
@@ -0,0 +1,33 @@
 <!DOCTYPE html>
 <html lang="en">
 <head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>P2P Poll</title>
  <link rel="stylesheet" href="/src/style.css">
 </head>
 <body>
  <div id="app">
    <header>
      <h1>P2P Poll</h1>
      <div id="status">
        <span id="connection-status" class="connecting">Connecting...</span>
        <span id="peer-count">1 peer</span>
      </div>
    </header>
    <main>
      <div id="add-option">
        <input type="text" id="option-input" placeholder="Add a poll option..." maxlength="100">
        <button id="add-btn">Add</button>
      </div>
      <div id="poll-options"></div>
      <p id="empty-state">No options yet. Add one above!</p>
    </main>
  </div>
  <script type="module" src="/src/main.js"></script>
 </body>
 </html>
--- a/package-lock.json
+++ b/package-lock.json
--- a/package.json
+++ b/package.json
@@ -1,20 +1,18 @@
 {
-  "name": "yjs-poll",
+  "name": "p2p-poll",
  "private": true,
  "version": "1.0.0",
  "main": "index.js",
  "type": "module",
  "scripts": {
-    "test": "echo \"Error: no test specified\" && exit 1",
+    "dev": "vite",
-    "y-websocket": "y-websocket"
+    "build": "vite build",
    "preview": "vite preview"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "description": "",
  "dependencies": {
-    "ws": "^8.19.0",
+    "yjs": "^13.6.0",
-    "@y/protocols": "^1.0.6-1",
+    "y-webrtc": "^10.3.0"
-    "lib0": "^0.2.102",
+  },
-    "yjs": "^14.0.0-7"
+  "devDependencies": {
    "vite": "^6.0.0"
  }
 }
--- a/src/main.js
+++ b/src/main.js
@@ -0,0 +1,136 @@
 import * as Y from 'yjs';
 import { WebrtcProvider } from 'y-webrtc';
 // --- Peer ID (stable across reloads) ---
 function getOrCreatePeerId() {
  let id = localStorage.getItem('peer-id');
  if (!id) {
    id = crypto.randomUUID();
    localStorage.setItem('peer-id', id);
  }
  return id;
 }
 const peerId = getOrCreatePeerId();
 // --- Room name from URL ---
 function getRoomName() {
  const params = new URLSearchParams(window.location.search);
  return params.get('room') || 'default-poll';
 }
 const roomName = getRoomName();
 // --- Yjs setup ---
 const ydoc = new Y.Doc();
 const provider = new WebrtcProvider(roomName, ydoc);
 const yOptions = ydoc.getMap('poll-options');
 // --- Data operations ---
 function addOption(name) {
  const id = crypto.randomUUID();
  const optionMap = new Y.Map();
  optionMap.set('name', name);
  optionMap.set('votes', new Y.Map());
  yOptions.set(id, optionMap);
 }
 function toggleVote(optionId) {
  const optionMap = yOptions.get(optionId);
  if (!optionMap) return;
  const votes = optionMap.get('votes');
  if (votes.has(peerId)) {
    votes.delete(peerId);
  } else {
    votes.set(peerId, true);
  }
 }
 // --- UI rendering ---
 const container = document.getElementById('poll-options');
 const emptyState = document.getElementById('empty-state');
 function render() {
  container.innerHTML = '';
  const entries = [];
  yOptions.forEach((optionMap, id) => {
    entries.push({
      id,
      name: optionMap.get('name'),
      votes: optionMap.get('votes').size,
      voted: optionMap.get('votes').has(peerId),
    });
  });
  entries.sort((a, b) => b.votes - a.votes || a.name.localeCompare(b.name));
  emptyState.className = entries.length > 0 ? 'hidden' : '';
  for (const entry of entries) {
    const div = document.createElement('div');
    div.className = 'poll-option';
    const nameSpan = document.createElement('span');
    nameSpan.className = 'option-name';
    nameSpan.textContent = entry.name;
    const voteCount = document.createElement('span');
    voteCount.className = 'vote-count';
    voteCount.textContent = entry.votes;
    const voteBtn = document.createElement('button');
    voteBtn.className = entry.voted ? 'vote-btn voted' : 'vote-btn';
    voteBtn.textContent = entry.voted ? 'Unvote' : 'Vote';
    voteBtn.addEventListener('click', () => toggleVote(entry.id));
    div.append(nameSpan, voteCount, voteBtn);
    container.appendChild(div);
  }
 }
 // Re-render on any change in the shared state
 yOptions.observeDeep(() => render());
 // --- Add option handlers ---
 const input = document.getElementById('option-input');
 const addBtn = document.getElementById('add-btn');
 addBtn.addEventListener('click', () => {
  const name = input.value.trim();
  if (name) {
    addOption(name);
    input.value = '';
  }
 });
 input.addEventListener('keydown', (e) => {
  if (e.key === 'Enter') addBtn.click();
 });
 // --- Connection status & peer count ---
 const statusEl = document.getElementById('connection-status');
 const peerCountEl = document.getElementById('peer-count');
 provider.on('synced', ({ synced }) => {
  statusEl.textContent = synced ? 'Connected' : 'Connecting...';
  statusEl.className = synced ? 'connected' : 'connecting';
 });
 function updatePeerCount() {
  const count = provider.awareness.getStates().size;
  peerCountEl.textContent = `${count} peer${count !== 1 ? 's' : ''}`;
 }
 provider.awareness.on('change', updatePeerCount);
 updatePeerCount();
 // --- Initial render ---
 render();
--- a/src/style.css
+++ b/src/style.css
@@ -0,0 +1,144 @@
 * {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
 }
 body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
  background: #f5f5f5;
  color: #333;
  min-height: 100vh;
 }
 #app {
  max-width: 600px;
  margin: 0 auto;
  padding: 2rem 1rem;
 }
 header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 2rem;
 }
 h1 {
  font-size: 1.5rem;
 }
 #status {
  display: flex;
  gap: 1rem;
  font-size: 0.85rem;
  color: #666;
 }
 #connection-status::before {
  content: "";
  display: inline-block;
  width: 8px;
  height: 8px;
  border-radius: 50%;
  margin-right: 4px;
  vertical-align: middle;
 }
 #connection-status.connected::before {
  background: #4caf50;
 }
 #connection-status.connecting::before {
  background: #ff9800;
 }
 #add-option {
  display: flex;
  gap: 0.5rem;
  margin-bottom: 1.5rem;
 }
 #option-input {
  flex: 1;
  padding: 0.6rem 0.8rem;
  border: 1px solid #ddd;
  border-radius: 6px;
  font-size: 1rem;
  outline: none;
 }
 #option-input:focus {
  border-color: #2196f3;
 }
 #add-btn {
  padding: 0.6rem 1.2rem;
  background: #2196f3;
  color: white;
  border: none;
  border-radius: 6px;
  font-size: 1rem;
  cursor: pointer;
 }
 #add-btn:hover {
  background: #1976d2;
 }
 .poll-option {
  display: flex;
  align-items: center;
  background: white;
  padding: 0.8rem 1rem;
  border-radius: 8px;
  margin-bottom: 0.5rem;
  box-shadow: 0 1px 3px rgba(0, 0, 0, 0.08);
 }
 .option-name {
  flex: 1;
  font-size: 1rem;
 }
 .vote-count {
  font-size: 0.9rem;
  font-weight: 600;
  color: #666;
  margin-right: 0.75rem;
  min-width: 1.5rem;
  text-align: center;
 }
 .vote-btn {
  padding: 0.4rem 1rem;
  border: 2px solid #2196f3;
  border-radius: 6px;
  font-size: 0.85rem;
  cursor: pointer;
  background: white;
  color: #2196f3;
 }
 .vote-btn:hover {
  background: #e3f2fd;
 }
 .vote-btn.voted {
  background: #2196f3;
  color: white;
 }
 .vote-btn.voted:hover {
  background: #1976d2;
 }
 #empty-state {
  text-align: center;
  color: #999;
  padding: 2rem;
 }
 #empty-state.hidden {
  display: none;
 }
--- a/utils.js
+++ b/utils.js
@@ -1,291 +0,0 @@
 /* Adapted from https://github.com/yjs/y-websocket-server/blob/main/src/server.js, version of 2025-04-02
   (author: dmonad/Kevin Jahns, MIT license) */
 import * as Y from 'yjs'
 import * as syncProtocol from '@y/protocols/sync'
 import * as awarenessProtocol from '@y/protocols/awareness'
 import * as encoding from 'lib0/encoding'
 import * as decoding from 'lib0/decoding'
 import * as map from 'lib0/map'
 import * as eventloop from 'lib0/eventloop'
 /*import { callbackHandler, isCallbackSet } from './callback.js'
 const CALLBACK_DEBOUNCE_WAIT = parseInt(process.env.CALLBACK_DEBOUNCE_WAIT || '2000')
 const CALLBACK_DEBOUNCE_MAXWAIT = parseInt(process.env.CALLBACK_DEBOUNCE_MAXWAIT || '10000')
 const debouncer = eventloop.createDebouncer(CALLBACK_DEBOUNCE_WAIT, CALLBACK_DEBOUNCE_MAXWAIT)*/
 const wsReadyStateConnecting = 0
 const wsReadyStateOpen = 1
 const wsReadyStateClosing = 2 // eslint-disable-line
 const wsReadyStateClosed = 3 // eslint-disable-line
 // disable gc when using snapshots!
 const gcEnabled = process.env.GC !== 'false' && process.env.GC !== '0'
 // const persistenceDir = process.env.YPERSISTENCE
 /**
 * @type {{bindState: function(string,WSSharedDoc):void, writeState:function(string,WSSharedDoc):Promise<any>, provider: any}|null}
 */
 let persistence = null
 /**
 * @param {{bindState: function(string,WSSharedDoc):void,
 * writeState:function(string,WSSharedDoc):Promise<any>,provider:any}|null} persistence_
 */
 export const setPersistence = persistence_ => {
  persistence = persistence_
 }
 /**
 * @return {null|{bindState: function(string,WSSharedDoc):void,
  * writeState:function(string,WSSharedDoc):Promise<any>}|null} used persistence layer
  */
 export const getPersistence = () => persistence
 /**
 * @type {Map<string,WSSharedDoc>}
 */
 export const docs = new Map()
 const messageSync = 0
 const messageAwareness = 1
 // const messageAuth = 2
 //const messageTextMessage = 3
 //const messageStateMessage = 4
 /**
 * @param {Uint8Array} update
 * @param {any} _origin
 * @param {WSSharedDoc} doc
 * @param {any} _tr
 */
 const updateHandler = (update, _origin, doc, _tr) => {
  const encoder = encoding.createEncoder()
  encoding.writeVarUint(encoder, messageSync)
  syncProtocol.writeUpdate(encoder, update)
  const message = encoding.toUint8Array(encoder)
  doc.conns.forEach((_, conn) => send(doc, conn, message))
 }
 /**
 * @type {(ydoc: Y.Doc) => Promise<void>}
 */
 let contentInitializor = _ydoc => Promise.resolve()
 /**
 * This function is called once every time a Yjs document is created. You can
 * use it to pull data from an external source or initialize content.
 *
 * @param {(ydoc: Y.Doc) => Promise<void>} f
 */
 export const setContentInitializor = (f) => {
  contentInitializor = f
 }
 export class WSSharedDoc extends Y.Doc {
  /**
   * @param {string} name
   */
  constructor (name) {
    super({ gc: gcEnabled })
    this.name = name
    /**
     * Maps from conn to set of controlled user ids. Delete all user ids from awareness when this conn is closed
     * @type {Map<Object, Set<number>>}
     */
    this.conns = new Map()
    /**
     * @type {awarenessProtocol.Awareness}
     */
    this.awareness = new awarenessProtocol.Awareness(this)
    this.awareness.setLocalState(null)
    /**
     * @param {{ added: Array<number>, updated: Array<number>, removed: Array<number> }} changes
     * @param {Object | null} conn Origin is the connection that made the change
     */
    const awarenessChangeHandler = ({ added, updated, removed }, conn) => {
      const changedClients = added.concat(updated, removed)
      if (conn !== null) {
        const connControlledIDs = /** @type {Set<number>} */ (this.conns.get(conn))
        if (connControlledIDs !== undefined) {
          added.forEach(clientID => { connControlledIDs.add(clientID) })
          removed.forEach(clientID => { connControlledIDs.delete(clientID) })
        }
      }
      // broadcast awareness update
      const encoder = encoding.createEncoder()
      encoding.writeVarUint(encoder, messageAwareness)
      encoding.writeVarUint8Array(encoder, awarenessProtocol.encodeAwarenessUpdate(this.awareness, changedClients))
      const buff = encoding.toUint8Array(encoder)
      this.conns.forEach((_, c) => {
        send(this, c, buff)
      })
    }
    this.awareness.on('update', awarenessChangeHandler)
    this.on('update', /** @type {any} */ (updateHandler))
    //if (isCallbackSet) {
    //  this.on('update', (_update, _origin, doc) => {
    //    debouncer(() => callbackHandler(/** @type {WSSharedDoc} */ (doc)))
    //  })
    //}
    this.whenInitialized = contentInitializor(this)
  }
 }
 /**
 * Gets a Y.Doc by name, whether in memory or on disk
 *
 * @param {string} docname - the name of the Y.Doc to find or create
 * @param {boolean} gc - whether to allow gc on the doc (applies only when created)
 * @return {WSSharedDoc}
 */
 export const getYDoc = (docname, gc = true) => map.setIfUndefined(docs, docname, () => {
  const doc = new WSSharedDoc(docname)
  doc.gc = gc
  if (persistence !== null) {
    persistence.bindState(docname, doc)
  }
  docs.set(docname, doc)
  return doc
 })
 /**
 * @param {any} conn
 * @param {WSSharedDoc} doc
 * @param {Uint8Array} message
 */
 const messageListener = (conn, doc, message) => {
  try {
    const encoder = encoding.createEncoder()
    const decoder = decoding.createDecoder(new Uint8Array(message))
    const messageType = decoding.readVarUint(decoder)
    switch (messageType) {
      case messageSync:
        encoding.writeVarUint(encoder, messageSync)
        syncProtocol.readSyncMessage(decoder, encoder, doc, conn)
        // If the `encoder` only contains the type of reply message and no
        // message, there is no need to send the message. When `encoder` only
        // contains the type of reply, its length is 1.
        if (encoding.length(encoder) > 1) {
          send(doc, conn, encoding.toUint8Array(encoder))
        }
        break
      case messageAwareness: {
        awarenessProtocol.applyAwarenessUpdate(doc.awareness, decoding.readVarUint8Array(decoder), conn)
        break
      }
      // If this is a text or a message (no Yjs logic) - echo the message back to the client
      default: {
        conn.send(String(message))
        console.log(String(message))
        break
      }
    }
  } catch (err) {
    console.error(err)
    // @ts-ignore
    doc.emit('error', [err])
  }
 }
 /**
 * @param {WSSharedDoc} doc
 * @param {any} conn
 */
 const closeConn = (doc, conn) => {
  if (doc.conns.has(conn)) {
    /**
     * @type {Set<number>}
     */
    // @ts-ignore
    const controlledIds = doc.conns.get(conn)
    doc.conns.delete(conn)
    awarenessProtocol.removeAwarenessStates(doc.awareness, Array.from(controlledIds), null)
    if (doc.conns.size === 0 && persistence !== null) {
      // if persisted, we store state and destroy ydocument
      persistence.writeState(doc.name, doc).then(() => {
        doc.destroy()
      })
      docs.delete(doc.name)
    }
  }
  conn.close()
 }
 /**
 * @param {WSSharedDoc} doc
 * @param {import('ws').WebSocket} conn
 * @param {Uint8Array} m
 */
 const send = (doc, conn, m) => {
  if (conn.readyState !== wsReadyStateConnecting && conn.readyState !== wsReadyStateOpen) {
    closeConn(doc, conn)
  }
  try {
    conn.send(m, {}, err => { err != null && closeConn(doc, conn) })
  } catch (e) {
    closeConn(doc, conn)
  }
 }
 const pingTimeout = 30000
 /**
 * @param {import('ws').WebSocket} conn
 * @param {import('http').IncomingMessage} req
 * @param {any} opts
 */
 export const setupWSConnection = (conn, req, { docName = (req.url || '').slice(1).split('?')[0], gc = true } = {}) => {
  conn.binaryType = 'arraybuffer'
  // get doc, initialize if it does not exist yet
  const doc = getYDoc(docName, gc)
  doc.conns.set(conn, new Set())
  // listen and reply to events
  conn.on('message', /** @param {ArrayBuffer} message */ message => messageListener(conn, doc, message))
  // Check if connection is still alive
  let pongReceived = true
  const pingInterval = setInterval(() => {
    if (!pongReceived) {
      if (doc.conns.has(conn)) {
        closeConn(doc, conn)
      }
      clearInterval(pingInterval)
    } else if (doc.conns.has(conn)) {
      pongReceived = false
      try {
        conn.ping()
      } catch (e) {
        closeConn(doc, conn)
        clearInterval(pingInterval)
      }
    }
  }, pingTimeout)
  conn.on('close', () => {
    closeConn(doc, conn)
    clearInterval(pingInterval)
  })
  conn.on('pong', () => {
    pongReceived = true
  })
  // put the following in a variables in a block so the interval handlers don't keep in in
  // scope
  {
    // send sync step 1
    const encoder = encoding.createEncoder()
    encoding.writeVarUint(encoder, messageSync)
    syncProtocol.writeSyncStep1(encoder, doc)
    send(doc, conn, encoding.toUint8Array(encoder))
    const awarenessStates = doc.awareness.getStates()
    if (awarenessStates.size > 0) {
      const encoder = encoding.createEncoder()
      encoding.writeVarUint(encoder, messageAwareness)
      encoding.writeVarUint8Array(encoder, awarenessProtocol.encodeAwarenessUpdate(doc.awareness, Array.from(awarenessStates.keys())))
      send(doc, conn, encoding.toUint8Array(encoder))
    }
  }
 }