Don't leak. Export.

If you export a function, the types of its arguments leak.

Even if your language of choice doesn’t allow you to write ReturnType<typeof f> and you can’t refer to them, their concept leaks and you need to be somewhat aware of it when using this function.

diff
- type Props = {
+ export interface ChatProps {
- export function Chat(props: Props) {
+ export function Chat(props: ChatProps) {

diff
- type Props = {
+ export interface ChatProps {
- export function Chat(props: Props) {
+ export function Chat(props: ChatProps) {

This is super important when you’re building a library: the consumer can’t trivially export your types, and on top of that there’s a risk of divergence whenever you change them and they bump a version.

But even if you’re building an app, you can save your coworkers some time and frustration if you explicitly export everything that’s getting leaked anyway.