javascript - Await socket.on('answerToRequest') possible with Socket.io? - Stack Overflow

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Is the following somehow possible?

async function doesSocketAgree(){
    socket.emit('doesOtherSocketAgree', otherSocketId);
    await socket.on('responseDoesSocketAgree', (answer)=>{
      console.log('answer');
});
}

Is the following somehow possible?

async function doesSocketAgree(){
    socket.emit('doesOtherSocketAgree', otherSocketId);
    await socket.on('responseDoesSocketAgree', (answer)=>{
      console.log('answer');
});
}

• javascript
• node.js
• websocket
• socket.io
• backend

Share Improve this question Follow asked Feb 17, 2020 at 23:58 Julian HackenbergJulian Hackenberg 12322 silver badges66 bronze badges

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2 Answers 2

Sorted by: Reset to default 6

In socket.io you can use "acknowledgements" callbacks:

async function doesSocketAgree(){
  await new Promise(resolve => {
    socket.emit('doesOtherSocketAgree', otherSocketId, (answer) => {
      resolve(answer);
    });      
  });
}

https://socket.io/docs/#Sending-and-getting-data-acknowledgements

So you can use a single emit() and can trigger a callback. That has the advantage you dont have to deal with memory leaks from register an event listener every time you call this function.

It is, but not that way. You'll have to wrap things in a promise so that you can "return" from your await once data es in as part of your "on" handling:

async function doesSocketAgree(){
  socket.emit('doesOtherSocketAgree', otherSocketId);
  await new Promise(resolve => {
    socket.on('responseDoesSocketAgree', answer => {
      resolve(answer);
    });
  });
}

And you probably want to remove that listener before you call resolve() so that it doesn't keep on triggering, because every time you call doesSocketAgree() you'd be adding a new listener to the "on:responseSocketAgree" pile. So that'll end up going wrong pretty quickly without cleanup.

On that note, you probably want to emit your "does it agree?" with a random token that your on handler can verify is the one that's scoped to the current function call, "because async".

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