This change makes the short option parsing work as intended, but changes the parse results and will be a breaking change for some users. (Albeit, as is any change!)

How likely is it that anyone will have been relying on the incorrect, and untested, results?

The potentially broken use case I have in mind is a short option value that for external reasons consistently ends in a number. A user might have discovered that the value could be put straight after the short option. For example:

enrol --course=COSC201
enrol -c COSC201
enrol -c=COSC201
enrol -cCOSC201   <-- only works like above due to bug

This might be rare since:

1. The README includes an example of short flags expanding into multiple individual flags, and using space separated values, so examples of how to use as intended. i.e. -x 3, -y 4, -n5, and -abc:

$ node example/parse.js -x 3 -y 4 -n5 -abc --beep=boop foo bar baz

2. The incorrect behaviour only happened for values ending in a number, so user might realise it was not a reliable way of supplying value even if they stumbled across it.

3. I don't recall issues mentioning the variant behaviour (but weak evidence, not sure how far back through the old open bugs I read or retained!).

I checked what yargs does, as the most evolved optimist descendent:

try-yargs $ node index.js -ABC123               
{ _: [], A: true, B: true, C: 123, '$0': 'index.js' }

Old minimist:

try-minimist $ node index.js -ABC123
{ _: [], flag: false, A: 'BC123' }

And on this branch minimist does:

$ node index.js -ABC123               
{ _: [], flag: false, A: true, B: true, C: 123 }

I agree this is better/more intuitive behavior. It would, however, be quite a breaking change.

Marking as semver-major (copied the label text and colours from qs)

If this comes up a lot in issues, or if we decide never to do a major, can reconsider.

This was reported as an issue on the original Minimist repo (comments from 2 users):

Parsing multiple short option with a default value
https://web.archive.org/web/20200904203146/https://github.com/substack/minimist/issues/50

node ../minimist/example/parse.js -ab1

{ _: [], a: 'b1' }

But the behavior I was expecting was: { _: [], a: true, b: 1 }

And a duplicate report on original Minimist repo:

Incorrectly parsed values while short param end with number
https://web.archive.org/web/20200904203609/https://github.com/substack/minimist/issues/103/

minimist(['-a2']) // => { _: [], a: 2 }  

minimist(['-abc']) // => { _: [], a: true, b: true, c: true }

minimist(['-abc2']) // => { _: [], a: 'bc2' }  why not { _: [], a: true, b: true, c: 2 }?