Value of React state not updating instantly

Question

I'm building a video calling feature into my app and the user's media stream is stored in a React state. However, when I try to access this state in another file (I'm using React Context for this), the stream state hasn't been updated yet and uses the default state value. I learnt, React updates state on the next render rather than instantly but I'm trying to access the stream instantly. However, I'm creating the Peer object inside a function so if I try to delay the stream access for example with a useEffect hook, I then can't use the function outside the hook. Are there any ways I could to this? Some code samples below:

Within context file: const [stream, setStream] = useState(null) Where I'm setting the stream:

useEffect(() => {
        navigator.mediaDevices.getUserMedia({ video: true, audio: true }).then((currentStream) => {
            setStream(currentStream);
        }).catch((error) => {
            console.log('Error accessing media devices: ', error);
        });
    }, []);

One of my functions (stream logs null):

function callUser(id) {
    console.log(stream)
    const peer = new Peer({ initiator: true, trickle: false, stream })

    peer.on('signal', (data) => {
      socket.emit('call-user', { userToCall: id, signalData: data, from: myID, name })
    })

    peer.on('close', () => {
      socket.off('call-answered')
      setCallAccepted(false)
      setCall(null)
      addCall(false)
      setInfoBarShow(false)
    })

    peer.on('stream', (currentStream) => {
      userVideo.current.srcObject = currentStream
    })

    socket.on('call-answered', (signal) => {
      setCallAccepted(true)

      peer.signal(signal)
    })

    socket.on('call-ended', (endReason) => {
      if (statusRef.current) {
        if (endReason === "declined" || endReason === "ended") statusRef.current.innerHTML = `Call ${endReason}`
      }
      setTimeout(() => {
        leaveCall()
      }, 5000)
    })

    connectionRef.current = peer
  }

I've tried lots of things such as wrapping the functions in a useEffect hook with the dependency as stream but then the functions aren't globally available. I've tried using selection but that won't work as the component still isn't being re-rendered/refreshed to include the updated state. Nothing works. For handling the WebRTC side of things I'm using the Simple-Peer package

To clarify: A button calls the function callUser. I'm accessing the stream state inside this function where I pass it into the Peer object for Simple-Peer. That stream value currently is using the default state of null that I set, not a MediaStream as it hasn't updated yet and that's my issue

Answer 1

It seems like you are dealing with the asynchronous nature of state updates in React. The issue you're facing is that the stream state is not immediately available when you are trying to use it in the callUser function. This is because the state update doesn't happen instantly, and your function is using the initial state value.

Use Context to Manage State:

import { createContext, useContext, useState } from 'react';

const StreamContext = createContext();

export const StreamProvider = ({ children }) => {
  const [stream, setStream] = useState(null);

  const setMediaStream = (newStream) => {
    setStream(newStream);
  };

  return (
    <StreamContext.Provider value={{ stream, setMediaStream }}>
      {children}
    </StreamContext.Provider>
  );
};

export const useStream = () => {
  return useContext(StreamContext);
};

Wrap App with Context Provider:

import React from 'react';
import ReactDOM from 'react-dom';
import App from './App';
import { StreamProvider } from './path of contextfile';

ReactDOM.render(
  <StreamProvider>
    <App />
  </StreamProvider>,
  document.getElementById('root')
);

Access Stream in Function:

import React from 'react';
import { useStream } from './path of contextfile';
import Peer from 'simple-peer';

function CallUserComponent() {
  const { stream } = useStream();

  const callUser = (id) => {
    // use the latest stream value
    console.log(stream);

    // your code
  };

  return (
    <button onClick={() => callUser('someUserId')}>Call User</button>
  );
}

export default CallUserComponent;