pass exclamation mark as prop value in react component

That a combination of:

• The optional chaining operator (?., TypeScript and JavaScript), and

• The non-null assertion operator (TypeScript) (really it's a non-nullish operator), which tells TypeScript that the resulting value is not either null or undefined.

The data?.list part gets the value of data.list if data is not null or undefined, or gets undefined if data is null or undefined. Then the ! asserts to TypeScript that the result of data?.list is not null or undefined (more below).

Note that this code is, at best, slightly confused. It makes no sense to use optional chaining and a non-nullish assertion, since the only reason for using optional chaining is to handle the case where the base (data) may be null or undefined and use the value undefined (instead of looking up .list) if so. Going on to assert that it's non-nullish doesn't make sense. One or the other of those shouldn't be there.

I'm guessing the ! is there because MyComponent doesn't allow its list prop to be null or undefined. If so, the code should be just:

<MyComponent list={data.list} />

...with appropriate logic beforehand to check that both data and data.list are not null or undefined or avoid rendering MyComponent at all if that's not true. For instance, perhaps:

{data?.list ? <MyComponent list={data.list} /> : null}