Formik: FastField doesn't set initial value with type="checkbox"

[MikeSuiter]

🐛 Bug report

Current Behavior

When using FastField and a checkbox's initial value is true the checkbox isn't checked. The code sandbox shows that Field works but FastField doesn't.

Expected behavior

Checked on true

Reproducible example

Your environment

| Software | Version(s) |
| ---------------- | ---------- |
| Formik | 2.1.4
| React | 16.12
| TypeScript |
| Browser | Safari, Chrome
| npm/Yarn | yarn 1.22
| Operating System | macOS Catalina

[pierreneter]

You must set checked={props.values.fastField}

[MikeSuiter]

That works but is it a workaround? I thought Field and FastField should act the same other than if the component should update? If you look at my original example Field works just fine without using the checked=value but FieldFast doesn't. I would think you could switch FastField and Field have the same functionality (other than if component should update).

[pierreneter]

Maybe they forgot to implement for type="checkbox"

[pieplu]

FastField define "field" props in different way than Field, and it's looks lik not complet:

https://github.com/jaredpalmer/formik/blob/c85d85a3b6236a30034e73f8b821a280de8856b0/packages/formik/src/FastField.tsx#L140-L148

value is set to undefined, but checked is not set for this cases....

[maddhruv]

Fixed with https://github.com/formium/formik/pull/2874