arrayformat as comma with empty array or objects

[davidlandais]

const options = {
  encode: false,
  strictNullHandling: true,
  arrayFormat: 'comma',
  allowDots: true,
  addQueryPrefix: true
};

const params = {
  foo: [],
  bar: [null],
  baz: ['abc'],
};

// with arrayFormat: 'comma'
qs.stringify(params, options);
// = ?foo=&bar=&baz=abc

// with arrayFormat: 'brackets'
// = ?bar[]&baz[]=abc

stringify will produce ?foo=&bar=&baz=abc. But using brackets, indices, repeat as array format will not concat foo cause it's an empty array. comma is the only one which keep foo. Is it a bug or a conception choice ?

In lib/stringify.js, line 67, maybe you could test if it's an array with values ?

[ljharb]

Are you suggesting that comma shouldn't include foo, or that the other three should?

[davidlandais]

Yes, i'm suggesting that comma shouldn't include foo :) All three other does not include it and i expected comma don't too. What do you think ?

[ljharb]

That seems reasonable to me.

[davidlandais]

Did you started or planing to workin on ? Cause if you need, when i got time, i will make you a pull request

[ljharb]

@davidlandais nope, help wanted means it's up for grabs :-) a PR would be great.

[kruchone]

I would like to offer my 2c on the opposite; I believe we should not strip the key out of the original object.
I am not sure qs should be assuming the intention of the empty array is to completely omit the query string entry entirely. I get that this is probably to-spec in HTTP but the reality is not all HTTP services are to-spec and this could cause problems if the intention of the caller is to actually send the blank query parameter. We are effectively stripping context out of the object when we remove the empty kv pairs.
I would argue that the caller could simply strip empty values before stringify even gets called if it really doesn't want them in the resulting string.

[ljharb]

@kruchone how to handle empty values seems like something that should be resolved in #226 - until then, i think it's important for all the arrayFormat options to behave the same.

[daggerjames]

It's a bug, I'll fix that later

[issuefiler]

Suggestion

There’s a use case where you have to convey the presence of an array, empty or not, and I find [null] rather counterintuitive for that purpose. I think there should be an option to specify the way qs handles empty arrays.

[ljharb]

@issuefiler what is one use case for that?

[jprosevear]

@issuefiler what is one use case for that?

An index REST api endpoint that takes filters that are query params in an 'in' style:
status=[1, 2, 3]

An empty array would filter to no elements but no query params (ie status=[] where qs would stringify as empty) would get all.