Data received from socket.io is not immediately reflected in the status

Question

When app.js receives data sent from the server (displayed in the console), setState does not refresh the web page with the new data. In the line console.log("Received data queue:", data.queue), it also returns undefined. I expected it to be a specific value because in the line console.log(data) it has the value stored under the "queue" key.

This is my code:

import React, { Component } from "react";
import { TransitionGroup, CSSTransition } from "react-transition-group";
import "./chat.css";
import "./styles.css";
import "./queue.css";
import Chat from "./chat";
import io from "socket.io-client";

class App extends Component {
  constructor(props) {
    super(props);
    this.state = {
      queue: [],
      instruction: "",
      user: "",
      hal: "",
      status: "waiting"
    };
  }
  componentDidMount() {
    const socket = io("http://localhost:5000");
    socket.on("connect", () => {
      console.log("Connected to the socket server");
    });

    socket.on("queueData", (data) => {
      console.log("Received data:", data);
      console.log("Received data queue:", data.queue);
      this.setState({ queue: data.queue }, () => {
        console.log(this.state.queue);
      });
      this.setState({ instruction: data.instruction }, () => {
        console.log(this.state.instruction);
      });
      // other attributes, user, hal, status ignored here for simplicity
    });

    this.socket = socket;
  }

  componentWillUnmount() {
    this.socket.disconnect();
  }


  renderData = () => {
    console.log("rendered queue", this.state.queue);
    if (this.state.queue === undefined) {
      return null;
    }
    return this.state.queue.map((task, index) => (
      
        

          {task}
          {index === 0 && this.state.status === "working" && (
            

          )}
        
      
    ));
  };

  render() {
    return (
      

        
        

          {this.renderData()}
          

            Instruction: {this.state.instruction}
          
        
      
    );
  }
}

export default App;

I want the webpage to refresh immediately when new data is received. I've added a callback function to setState, but it still doesn't work.

Answer 1

When using socket.io in your application, you may experience delays in updating status after receiving data due to a number of factors. For example, the asynchronous nature of socket.io, state management issues, event handling, React component life cycle, etc.