# Sending flow validation (cont.) - Fri 6th Nov, 2020 Continued with sending flow validation. Below are a few learnings. Use `Exclude` in TypeScript to exclude a type from a union: ```typescript= Exclude<MyType, 'thing'> ``` Biggest takeaway (and something I lost quite a few hours to) is [how Formik handles setFieldTouched and setFieldValue](https://github.com/formium/formik/issues/2083) from the `useFormikContext` hook. This is not a bug with Formik, but simply how React works. The solution (unfortunately) is to use a `setTimeout` to force `setFieldTouched` to the end of the event loop: ```typescript= setTimeout(() => setFieldTouched('recipients', true)) setFieldValue('recipients', values.recipients.filter((recipient) => recipient.id !== user.id) ) ``` ###### tags: `programmingjournal` `2020` `C+` `validation` `useFormikContext` `setTimeout` `setFieldTouched` `exclude`