[seanwilson]

> It's already easy to see that submitter is optional.

Why force yourself to read inside function implementations like this for every function you might use when fool-proof automated assistance is right there? What if the function was tens of lines long? What if the optional value only appeared inside a chain of 5 nested functions? How would you easily fix/update your code if the value isn't optional now but got changed to be optional in the future?

Manual effort like this is error-prone, not scalable, and a huge distraction. Why would avoiding type annotations be worth this?

[benatkin]

Because this is an internal function in a _library_, and you should be willing to look inside it if you're changing a call to it.

Here's where whether or not it's defined can be traced to: https://github.com/hotwired/turbo/blob/41c074ff113a8882aadbc...

Maybe the types should have been written differently, to indicate that it's the type of the submitter property in a FormEvent. That's another cost of using TypeScript, is trying to get the types right. TMTOWTDI.

[seanwilson]

> Because this is an internal function in a _library_

Why does that matter? Error-prone approaches create buggy code and we don't want buggy code, whether it's a library or something else. Libraries can be huge and complex, and arguably should have more robust edge case checking than regular code.