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How get notifications from stack overflow for new questions?

I would like to answer to new javascript, react, react-native and node questions. So, how would I know about the new questions which are asked by users on these areas?

Answer

Open a Websocket connection to wss://qa.sockets.stackexchange.com/, then send the message 1-questions-newest-tag-TAG where TAG is the tag you want to watch for. When a new question is posted, you’ll be sent a message with the question ID.

The question data needs to be retrieved separately (as of SE’s winter 2021/2022 redesign). One way to do it – as SE does it on /newest pages – is to POST to /posts/ajax-load-realtime-list/ with the question ID, and it will respond with the question summary. (Unfortunately, due to cross-origin restrictions, this approach can’t be embedded into a live Stack Snippet)

Open a blank page on Stack Overflow, such as this one, and then paste the following into your console, and you’ll see new questions appear on the page as they’re posted:

const socket = new WebSocket('wss://qa.sockets.stackexchange.com/');
socket.onopen = () => {
  socket.send('1-questions-newest-tag-javascript');
  socket.send('1-questions-newest-tag-java');
  socket.send('1-questions-newest-tag-python');
  socket.send('1-questions-newest-tag-php');
  console.log('Listening...');
};
const seenQuestions = new Set();
socket.onmessage = ({ data }) => {
  const obj = JSON.parse(data);
  if (obj.action === 'hb') {
    socket.send('pong');
    return;
  }
  const { id, body } = JSON.parse(obj.data);
  if (seenQuestions.has(id)) {
    // Duplicate question, a message for it has already been handled:
    return;
  }
  seenQuestions.add(id);
  console.log('New question:', id);
  insertQuestion(id)
};
socket.onerror = console.error; // just in case

const insertQuestion = (questionId) => {
  const params = new URLSearchParams();
  params.append('postIdsSemiColonDelimited', questionId);
  fetch('https://stackoverflow.com/posts/ajax-load-realtime-list/', {
    method: 'post',
    body: params
  })
    .then(r => r.json())
    .then((result) => {
      document.body.insertAdjacentHTML('beforeend', result[questionId]);
    })
    .catch(console.error); // just in case
};

If you want to use this anywhere else other than on a Stack Exchange site, you might also wish to embed their CSS

You do need to listen for a hb message and reply to it, so that StackExchange knows to keep the connection alive.

Do note that the socket will send data for a given question for every tag being listened for. Eg, if something is tagged with both Javascript and React, and you’ve sent requests to listen for both tags, you’ll receive a message for that twice, hence the need for the Set to avoid listing duplicates.