Develop a Streaming Chat App in React.js with Langchain

Creating a streaming chat application with language support ensures seamless communication among users from different language backgrounds. In this article, we will be using React.js and Langchain to develop a chat application that supports real-time translation, enhancing the user experience.

Table of Contents

  1. Introduction to React.js and Langchain
  2. Setting Up the Project
  3. Building the Chat Interface
  4. Adding Language Support with Langchain
  5. Connecting and Testing the Streaming Chat
  6. Conclusion

Introduction to React.js and Langchain

React.js is a popular JavaScript library for building user interfaces. It is especially useful for developing single-page applications, where data can update without refreshing the page.

Langchain is a translation-as-a-service platform that offers real-time translation for chat applications. It enables users to communicate across different languages, making it an excellent choice for our streaming chat application.

Setting Up the Project

  1. Install Node.js and npm (Node Package Manager) if you haven't already. You can download them from the official website.

  2. Install Create React App globally using the following command:

npm install -g create-react-app
  1. Create a new React project using Create React App:
create-react-app streaming-chat-app
  1. Navigate to the project directory:
cd streaming-chat-app
  1. Install the necessary dependencies:
npm install langchain

Building the Chat Interface

We will create a simple chat interface using React components:

  1. Create a new folder called components inside the src folder.

  2. Inside the components folder, create a new file called Chat.js.

  3. Add the following code to Chat.js:

import React, { useState, useEffect } from 'react';
import { io } from '';

const Chat = () => {
  const [message, setMessage] = useState('');
  const [messages, setMessages] = useState([]);
  const [socket, setSocket] = useState(null);

  useEffect(() => {
    const newSocket = io('http://localhost:3001');
    newSocket.on('message', (msg) => {
      setMessages((prevMessages) => [...prevMessages, msg]);
    return () => newSocket.close();
  }, []);

  const sendMessage = () => {
    if (socket) {
      socket.emit('message', message);

  return (
        {, index) => (
          <li key={index}>{msg}</li>
      <input value={message} onChange={(e) => setMessage(} />
      <button onClick={sendMessage}>Send</button>

export default Chat;

Adding Language Support with Langchain

  1. Import the Langchain library at the top of Chat.js:
import Langchain from 'langchain';
  1. Create a Langchain instance with your API key:
const langchain = new Langchain(<your-api-key>);
  1. Modify the sendMessage function to send a translated message:
const sendMessage = async () => {
  if (socket) {
    const translatedMessage = await langchain.translate(message, 'en', 'es');
    socket.emit('message', translatedMessage);
  1. Update the newSocket.on('message', ...) event listener to handle translated messages:
newSocket.on('message', async (msg) => {
  const translatedMessage = await langchain.translate(msg, 'es', 'en');
  setMessages((prevMessages) => [...prevMessages, translatedMessage]);

Connecting and Testing the Streaming Chat

  1. Replace the content of src/App.js with the following code:
import React from 'react';
import Chat from './components/Chat';

function App() {
  return (
    <div className="App">
      <Chat />

export default App;
  1. Start the React development server:
npm start
  1. Open your browser and navigate to http://localhost:3000. You should now see the chat interface.

  2. Test the streaming chat by sending messages between two different browsers or devices.


In this article, we learned how to create a streaming chat application in React.js with language support using Langchain. This allows users to communicate seamlessly across different languages, enhancing their experience. You can further expand the application by adding user authentication, additional language options, and more. Happy coding!

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