Hacker News

  try {
    // Parallel execution of independent operations
    const [config, userData] = await Promise.all([
      readFile('config.json', 'utf8'),
      fetch('/api/user').then(r => r.json())
    ]);
    ...
  } catch (error) {
    // Structured error logging with context
    ...
  }

This might seem fine at a glance, but a big grip I have with node/js async/promise helper functions is that you can't differ which promise returned/threw an exception.

In this example, if you wanted to handle the `config.json` file not existing, you would need to somehow know what kind of error the `readFile` function can throw, and somehow manage to inspect it in the 'error' variable.

This gets even worse when trying to use something like `Promise.race` to handle promises as they are completed, like:

  const result = Promise.race([op1, op2, op3]);

You need to somehow embed the information about what each promise represents inside the promise result, which usually is done through a wrapper that injects the promise value inside its own response... which is really ugly.

augusto-moura 2 days ago [ - ]

You are probably looking for `Promise.allSettled`[1]. Which, to be fair, becomes quite convulated with destructuring (note that the try-catch is not necessary anymore, since allSettled doesn't "throw"):

  // Parallel execution of independent operations
  const [
    { value: config, reason: configError },
    { value: userData, reason: userDataError },
  ] = await Promise.allSettled([
    readFile('config.json', 'utf8'),
    fetch('/api/user').then(r => r.json())
  ]);

  if (configError) {
    // Error with config
  }

  if (userDataError) {
    // Error with userData
  }

When dealing with multiple parallel tasks that I care about their errors individually, I prefer to start the promises first and then await for their results after all of them are started, that way I can use try catch or be more explicit about resources:

  // Parallel execution of independent operations
  const configPromise = readFile('config.json', 'utf8')
  const userDataPromise = fetch('/api/user').then(r => r.json())

  let config;
  try {
    config = await configPromise
  } catch (err) {
    // Error with config
  }

  let userData;
  try {
    userData = await userDataPromise
  } catch (err) {
    // Error with userData
  }

Edit: added examples for dealing with errors with allSettled

[1]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe...

SebastianKra 2 days ago [ - ]

IMO when you do control-flow in catch blocks, you're fighting against the language. You lose Typescripts type-safety, and the whole "if e instanceof ... else throw e"-dance creates too much boilerplate.

If the config file not existing is a handleable case, then write a "loadConfig" function that returns undefined.