CODEWITHSUNDEEP
javascripteventspromisedom-eventses6-promise
uzyn
uzyn

Reputation: 6693

Combining Promise with Events

How should a Promise async function be done combining with event?

function f() {
  return promisedFunction().then(event => {
    let buf = '';
    event.on('data', data => {
      buf += data.toString()
    });
    event.on('end', () => {
      return buf;
    });
    // how should I return buf here so that the promise would resolve fine?
  });
}

Upvotes: 1

Views: 286

Answers (1)

T.J. Crowder
T.J. Crowder

Reputation: 1074355

This is one of those few situations where you can't avoid creating a new promise. You'd do that in then and return it:

function f() {
  return promisedFunction().then(event => {
    return new Promise((resolve, reject) => {
      let buf = '';
      event.on('data', data => {
        buf += data.toString()
      });
      event.on('end', () => {
        resolve(buf);
      });
      event.on(/*...presumably there's an error condition?...*/, () => {
        reject(/*..details of error..*/);
      });
    });
  });
}

Easily 90% of the time, you already have a promise to work with (and one of the most common errors with promise is creating them when you don't have to), but you don't have one you can use to wait for the events in your example.

Upvotes: 5

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