Undocumented breaking change (now incompatible with caolan/async)

[mathiasm74]

The code below works with caolan/async v3.2.0 and with suguru03/neo-async v1.8.2 and outputs

Arguments passed from 'each()' callback: [Arguments] { '0': [Function] }
Arguments passed from 'waterfall()' callback: [Arguments] { '0': null }

However after updating suguru03/neo-async to v2.6.2 it will crash, and only work if the "res" argument is added to the "step2" function. The output is now different:

Arguments passed from 'each()' callback: [Arguments] { '0': undefined, '1': [Function: next] }
Arguments passed from 'waterfall()' callback: [Arguments] { '0': null, '1': undefined }

It appears this breaking changes was introduced by the new once() methods in

commit bd0fb377579bcd83b7ef5b155bf55668c6b4788f
Author: Suguru Motegi <[email protected]>
Date:   Sat Sep 29 19:49:26 2018 -0700

and the original behaviour seems to be correct and desired, since the new argument is always 'undefined'.

Here's the test code:

const order = [];
const array = [1, 3, 2];

async.waterfall([
  function step1(callback) {
    async.each(
      array, 
      function iterator(num, done) {
        setTimeout(function() {
          order.push(num);
          done();
        }, num * 10);
      }, 
      callback
    );
  },
  function step2(/*res, */callback) {
    console.log("Arguments passed from 'each()' callback:", arguments);
    callback(null);
  }
], function done(err) {
  console.log("Arguments passed from 'waterfall()' callback:", arguments);
  process.exit();
});

[suguru03]

@mathiasm74
Thanks for the issue!

I would like to fix it, however, the fix would affect a lot of users… so I will fix it on the next major update.