How can I add a class to a button when a Formik Form isSubmitting?

Question

How can I add a class to a button when a Formik Form isSubmitting?

I can see rendering different text if the form isSubmitting eg {isSubmitting ? "Please wait..." : "LOG IN"} {isSubmitting ? "Please wait..." : "LOG IN"} - but how can I add a class/ className to the button?

<button
    type="submit"
    className={`btn`}
    onClick={() => {
    api.submitForm();
    }}
    disabled={api.isSubmitting}
>
    LOG IN
</button>

Answer 1

You can simply do

className={'btn ' + (isSubmitting ? 'btn-while-submitting' : '')}

Or using something like classnames

className={classNames('btn', {
    ['btn-while-submitting']: isSubmitting,
})}