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Building a Real-Time Collaborative Document Editor with Svelte and Serverless Functions

Majd Muhtaseb06/23/202510 minutes

Introduction

Real-time collaborative document editors are becoming increasingly popular. This article demonstrates how to build a basic version using Svelte for the frontend and serverless functions for the backend, enabling real-time updates across multiple users.

Project Setup

First, create a new SvelteKit project:

npm create svelte@latest my-collab-editor
cd my-collab-editor
npm install

Frontend (Svelte)

Create a component, Editor.svelte, to handle the document editing:

<script>
  import { onMount } from 'svelte';

  let text = '';
  let socket;

  onMount(() => {
    socket = new WebSocket('ws://localhost:3000'); // Replace with your serverless function WebSocket endpoint

    socket.onopen = () => {
      console.log('Connected to WebSocket');
    };

    socket.onmessage = (event) => {
      text = event.data;
    };

    socket.onclose = () => {
      console.log('Disconnected from WebSocket');
    };
  });

  function handleInput() {
    socket.send(text);
  }
</script>

<textarea bind:value={text} on:input={handleInput} />

Place the Editor.svelte component inside routes/+page.svelte.

Backend (Serverless Function - Example with Node.js)

This example uses a simple WebSocket server. You would need to adapt it to your chosen serverless platform.

// server.js (Example - adapt for your serverless environment)
const WebSocket = require('ws');
const wss = new WebSocket.Server({ port: 3000 });

let sharedText = '';

wss.on('connection', ws => {
  console.log('Client connected');
  ws.send(sharedText); // Send current state upon connection

  ws.on('message', message => {
    sharedText = message.toString();
    wss.clients.forEach(client => {
      if (client !== ws && client.readyState === WebSocket.OPEN) {
        client.send(sharedText);
      }
    });
  });

  ws.on('close', () => {
    console.log('Client disconnected');
  });
});

console.log('WebSocket server started on port 3000');

Important: Adapting this for serverless environments (Netlify Functions, AWS Lambda) requires using an API Gateway and a WebSocket management service like AWS API Gateway with WebSocket support or similar solutions offered by your cloud provider. The serverless function needs to handle WebSocket connections and message routing.

Explanation

• Frontend (Svelte): The Editor.svelte component establishes a WebSocket connection with the serverless function. Whenever the text area's content changes (handleInput), it sends the updated text to the server. It also listens for incoming messages from the server (socket.onmessage) and updates the text area accordingly.

• Backend (Serverless Function): The serverless function (in the simplified example above) listens for WebSocket connections. Upon connection, it sends the current shared text to the new client. When a message is received, it updates the sharedText and broadcasts it to all connected clients except the sender, ensuring everyone has the latest version.

Considerations

• Real Serverless Implementation: The server-side code provided is for demonstration purposes. For a true serverless implementation, you need to leverage a cloud provider's API Gateway and WebSocket management service.
• Scalability: Carefully design your serverless architecture for scalability and cost-effectiveness. Consider using databases to persist document history and provide version control.
• Conflict Resolution: The current implementation doesn't handle concurrent edits effectively. Implementing Operational Transformation (OT) or Conflict-free Replicated Data Types (CRDTs) is crucial for robust collaborative editing.
• Authentication: Add authentication to restrict access to documents.
• Error Handling: Implement proper error handling on both the client and server sides.

Conclusion

This article provided a basic framework for building a real-time collaborative document editor with Svelte and serverless functions. While it's a simplified version, it highlights the fundamental concepts involved. Building a production-ready editor requires addressing the considerations mentioned above for scalability, conflict resolution, and security.