Is there an option to prevent value of the same key being populating into an array?

[leoyli]

Hi there,

I'm trying to figure out if qs.parse allow us to update the query key value instead of collecting those as an array from the doc, but I can not find anything about that so I'm asking here.

By default,

qs.parse('?num=1&num=2') === { num: ['1', '2'] };

Instead, I just care about the last value assigned to num in the query. i.e.

qs.parse('?num=1&num=2', { some_option: true }) === { num: '2' };

Is there a some_option to do so?

I'm working on an API and want a consistent way to handle the value. It is annoying to check if the query value is an array for a given key every single time (and it can be an object sometimes)... and at this point I decided to ignore all other value but the latest bound to the key.

But I guess people may also want only the first key value is preserved?! (e.g. that is how StarkOverflow handled their duplicated query key.)

Thanks!

[ljharb]

One common way it's done is that array keys always have a [] at the end of the name - that's how PHP and Rails do it, for example.

I don't believe there's currently an option to treat duplicate non-array keys as "last one wins" (I don't think "first one wins" would make any sense).

However, since in my experience the most typical webserver setups are:

1. a=1&a=2 gives a as 2 (a[]=1&a[]=2 gives a as [1, 2])
2. a=1&a=2 gives a as [1, 2] (a[]=1&a[]=2 gives a as [1, 2])

it seems like a reasonable option to add to parse. For stringify, you'd want the arrayFormat: brackets option (using "repeat" with this new parsing option would lose information).

[leoyli]

@ljharb Yeah

I see. I currently just added a function to modify the result from qs.parse() in my express app for recursivly handling the last-one-win case (so that I don't need to check if it is a string or array every time, and being safely use string method upon the value of a key).

If add this option is considered, then I actually would suggest to also support first-one-win as an option. It was rarely seemed, but some website does it, e.g. StackOverflow.

[ThiefMaster]

There should also be an option to do the exact opposite, i.e. always create an array. That would make code easier that expects 1 or more values for an option - currently I need to check if it's an array and otherwise create one from it.

[617dev]

@leoyli I would say this should be the default behavior, and an option to always create an array should be added for those that want that... i'm dealing with a prod bug caused by this unexpected behavior right now...

[dreyks]

I think there should be an arrayFormat for parse the same way it is for stringify, so that you can specify brackets/commas/repeat

As a partial workaround however a repeat option would work too - set it to true by default to avoid breaking changes. Setting it to false will make each same key override the previous one unless it's a bracket.
something like this, instead of

qs/lib/parse.js

Lines 90 to 94 in e39c235

	if (has.call(obj, key)) {
	obj[key] = utils.combine(obj[key], val);
	} else {
	obj[key] = val;
	}

we can do

if (has.call(obj, key) && (bracketEqualsPos !== -1 || options.repeat)) {
  obj[key] = utils.combine(obj[key], val);
} else {
  obj[key] = val;
}

that way

qs.parse('a=1&a=2') === { a: [1, 2] } // same as it is right now
qs.parse('a=1&a=2', { repeat: false }) === { a: 2 }

WDYT?

[ljharb]

@dreyks it makes sense to me to try to make the APIs of parse and stringify more consistent; if you think you could draft a PR with tests that does that for arrayFormat, i'd be happy to review it.

[dreyks]

gonna give it a try when time allows

[dreyks]

#329