handleChange type doesn't work

[olso]

Bug report

Current Behavior

no type error with

onChange(v: number)

Expected behavior

with this commented

we finally get type error

Reproducible example

Suggested solution(s)

https://github.com/formium/formik/blob/80f9a831797429ae3c4457a47b6d8391e9d8bd2c/packages/formik/src/types.tsx#L140-L145

modify preact-like typing

Additional context

Your environment

Software	Version(s)
Formik	2.2.6
React	17.0.1
TypeScript	4.0.5
Browser	Any
npm/Yarn	1.22.4
Operating System	Big Sur

[johnrom]

You would have to pass onChange={handleChange("lengthMeterTo")} so it would automatically pass your value back to the field itself.

If that callback is typed with a string, that would be an issue. It should be any. If you need a typescript fix, you can accomplish this right now in a child component of Formik with:

const [{ onChange }] = useField<number>("lengthMeterTo");

// this onChange expects a number.
<YourInput onChange={onChange} />

What you're requesting for handleChange is actually impossible to completely type. Even though you suggest "kind of" typing it, it doesn't type it based off of Values and name, so it is an incomplete type. We're trying to figure out how to give full typing to values and all related callbacks based on name, and have had some success with #1334 #2655 but nothing to merge just yet. Our successful tries require bleeding edge TypeScript, which we're not going to depend on just yet. Probably targeted for v3.

[olso]

Thanks for getting back to me, that solution works for me!

[johnrom]

Duplicate of #2084 at al