Implement useEffect on for subscribing to a real-time data stream

Implement useEffect on for subscribing to a real-time data stream

Let's consider a real-time example of using useEffect for subscribing to a real-time data stream. In this example, we'll use the WebSocket API to connect to a WebSocket server and receive real-time updates.

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

function RealTimeDataExample() {
  // State variable
  const [realTimeData, setRealTimeData] = useState(null);

  // useEffect for setting up the WebSocket connection
  useEffect(() => {
    // Create a WebSocket connection
    const socket = new WebSocket('wss://');

    // Event listener for handling incoming messages
    const handleWebSocketMessage = (event) => {
      const newData = JSON.parse(;

    // Event listener for handling errors
    const handleWebSocketError = (event) => {
      console.error('WebSocket error:', event);

    // Add event listeners to the WebSocket
    socket.addEventListener('message', handleWebSocketMessage);
    socket.addEventListener('error', handleWebSocketError);

    // Clean-up function (componentWillUnmount)
    return () => {
      // Close the WebSocket connection when the component is unmounted
  }, []); // Empty dependency array means this effect runs once after the initial render

  // Render based on real-time data
  return (
      <h1>Real-Time Data</h1>
      {realTimeData ? (
        <pre>{JSON.stringify(realTimeData, null, 2)}</pre>
      ) : (
        <p>Waiting for real-time updates...</p>

export default RealTimeDataExample;

In this example:

  • We have a componentRealTimeDataExample that connects to a WebSocket server using the WebSocket API.

  • TheuseEffect hook is used to set up the WebSocket connection. It adds event listeners for handling incoming messages and errors.

  • ThehandleWebSocketMessage function parses the incoming JSON data and updates the component's state with the real-time data.

  • The clean-up function (return () => {...}) ensures that the WebSocket connection is closed when the component is unmounted.


This example demonstrates how useEffect can be used to handle real-time updates, such as those from a WebSocket or other asynchronous data sources. The component sets up the connection when it mounts and cleans up the connection when it unmounts.