implement console.trace()

[40detectives]

Could it be possible to implement console.trace? Right now the method is present in the console object but returns undefined (if you check them to be shown).

[lukehaas]

👍 will be good to have this at some point.

[oculus42]

This is still a minor item, but it has come up for me lately. I've been testing a proof-of-concept promise tracer. This would mostly be for demonstration in RunJS, being able to demonstrate the functionality would be nice.

My example code, for reference:

const tracePromise = (promise, options, depth=0) => ({
  get then() {
    if (options.then !== false) {
      console.log(`${options.message ?? ''} .then() depth ${depth} accessed`);
      if (options.trace) console.trace();
    }
    if (!options.deep) return promise.then.bind(promise);
    return function (...args) {
      return tracePromise(promise.then(...args), options, depth+1);
    }
  },
  get catch() {
    if (options.catch !== false) {
      console.log(`${options.message ?? ''} .catch() depth ${depth} accessed`);
      if (options.trace) console.trace();
    }
    if (!options.deep) return promise.catch.bind(promise);
    return function (...args) {
      return tracePromise(promise.catch(...args), options, depth+1);
    }
  },
});

const one = () => {
  console.log('one');
  const { promise, resolve } = Promise.withResolvers();
  setTimeout(resolve, 0, 3);
  return tracePromise(promise, { message: 'one', trace: true, deep: true });
};

const two = () => {
  console.log('two');
  return one().then((v) => v * 2);
};

const three = (v) => {
  console.log('three');
  return two().then((data) => data * v);
};

three(3).then(console.log).catch(console.error);

The current output shows the console.log entries, but not the trace.

'three'
'two'
'one'
'one .then() depth 0 accessed'
'one .then() depth 1 accessed'
'one .then() depth 2 accessed'
'one .catch() depth 3 accessed'
'one .then() depth 4 accessed'
18

An example with file imports would probably be more interesting than the many "VM" entries my example provides in Chrome, but being able to see the trace in RunJS would be nice.