how to validate field only when it exists?

I would like to know how do I validate a field only when it exists.

My problem is that I have a phone field, but this field is dynamic and may or may not exist in the DOM, and I would like to validate it in my schema when it exists, but the problem is that when I put phone: Yup.string ().Required(), these fields are stuck in the validation even if they do not exist in the DOM.

Any suggestions to escape this validation?

[kevinjanczak-dev]

const schema = yup.object({
    phone: yup.string().when('$exist', {
        is: exist => exist,
        then: yup.string().required(),
        otherwise: yup.string()
    })
})

schema.validate({  }, {
    context: { exist: false }
}).catch(err => console.log(err))

[jrmarqueshd]

UPDATE:

In the version 0.32.11, the solution of @kevinjanczak-dev is not working.

And a found a solution to make validaiton only when field value exists, i’m using Cyclic Dependency, and this is my code:

const schema = yup.object().shape(
	{
		phone: yup.string().when('phone', {
			is: (exists) => !!exists,
			then: yup.string().test('validate_phone', 'phone is invalid', (phone) => phone.length === 14),
			otherwise: yup.string(),
		}),
	},
	[['phone', 'phone']],
);