Allow empty string but fail on undefined

[scholtzm]

According to README, it should be possible to require empty string:

To allow empty strings but fail on undefined values use: string().required().min(0)

However, this does not seem to work:

const yup = require("yup")

const okString = 'foo';
const shouldBeOkString = '';
let nokString;

const schema = yup.string().required().min(0);

console.log(await schema.isValid(okString)); // true
console.log(await schema.isValid(shouldBeOkString)); // false <--
console.log(await schema.isValid(nokString)); // false

Same with yup.array().required().min(0) won't allow [].

Am I missing something?

[scholtzm]

Don't want to create another issue so here's another example:

const yup = require("yup")

// want to accept any number or null, nothing else
const schema = yup.number().required().nullable(true);

console.log(await schema.isValid(1)); // true
console.log(await schema.isValid(23)); // true
console.log(await schema.isValid(null)); // false <--
console.log(await schema.isValid(undefined)); // false

[jquense]

So required will always fail for absent values, e.g. null or undefined. If you want to distinguish between them you'll need a more nuanced test:

yup.addMethod(yup.mixed, 'defined', function (msg = '$path must be defined') {
   return this.test('defined', msg, (value) => value !== undefined)
})

const schema = yup.number().defined().nullable();

console.log(await schema.isValid(1)); // true
console.log(await schema.isValid(23)); // true
console.log(await schema.isValid(null)); // false <--
console.log(await schema.isValid(undefined)); // false

[scholtzm]

Thank you @jquense. This solution fixes the case from my additional comment.

What about the required().min(0) case?

[jquense]

should work in that case as well. if you are only interesting in undefined failing it, you don't want to use required

[scholtzm]

Thank you, it indeed solves my issue.

However, are these sentences from the README valid?

To allow empty strings but fail on undefined values use: string().required().min(0)

In this case, '' will not pass the test.

To allow empty arrays but fail on undefined values use: array().required().min(0)

In this case, [] will not pass the test.

[jquense]

yeah they seem outdated, care to PR removing them?

[scholtzm]

Alright, see PR #137

[tnrich]

I don't see how to do the old

string().required().min(0) 

case anymore. Do I have to now provide a custom yup method? I made a SO question asking for help https://stackoverflow.com/questions/63943689/how-to-get-yup-string-to-require-string-of-any-length-including-0

Thanks!

[blasterbug]

In deed, string().required().min(0) fail miserably for empty strings.