prepareDataForValidation turns a nested array into an object

[agmcleod]

🐛 Bug report

Current Behavior

I have a fairly large complex data shape that goes into the form i'm working on, but the example piece is like this:

{
  tableData: [
    ['1', '2']
  ]
}

Then when it runs through the validation function, it has the wrong shape by the time it reaches yup.

{
  tableData: [
    { 0: '1', 1: '2' }
  ]
}

Can find the source for this here: https://github.com/jaredpalmer/formik/blob/master/src/Formik.tsx#L994. Since it's using for in, it's treated as an object regardless if it's an array or not.

Expected behavior

I'd like it so the shape remains the same, and it can validate against my yup validation:

let scheme = yup.array().of(
  yup
    .array()
    .of(yup.string().required('Is required'))
    .required()
)

Reproducible example

I tried running the code sandbox, but it seems to be giving me zero validation errors. https://codesandbox.io/s/formik-codesandbox-template-dtyw2

Suggested solution(s)

Maybe not the cleanest approach, but i would probably just iterate the array differently from the object. Use Object.keys for an object, and if Array.isArray() returns true, use a for loop or .forEach instead.

Your environment

Software	Version(s)
Formik	2.0.3
React	16.9.0
TypeScript	n/a
Browser	Firefox
npm/Yarn	1.13.0
Operating System	Mac OS 10.14.5 (mojave)