no-callback-in-promise.md

Pattern: Callback in Promise handler

Issue: -

Description

Calling callbacks inside Promise handlers (.then() or .catch()) can lead to unexpected behavior like multiple invocations. Keep async code consistent by using either promises or callbacks, not both.

Examples

Example of incorrect code:

function processWithCallback(callback) {
  Promise.resolve(data)
    .then(() => callback(null, result))
    .catch(err => callback(err));
}

Example of correct code:

// Using promises
async function process() {
  try {
    const result = await Promise.resolve(data);
    return result;
  } catch (err) {
    throw err;
  }
}

// Or using callbacks
function processWithCallback(callback) {
  try {
    callback(null, result);
  } catch (err) {
    callback(err);
  }
}