[TypeScript] correct way to tell typescript a property does exist?

I have the following function;

function myfunc<T extends MyInterface>(item: T) {
  if ("somekey" in item) console.log(item.someKey) // Error property does not exist
}

function myfunc<T extends MyInterface>(item: T) {
  if ("somekey" in item) console.log(item.someKey) // Error property does not exist
}

Is there a proper way to inform typescript that inside of that if block, by definition, that property very much does exist? or is this a case where TS is painfully blind to reality?

4 Replies

Unknown User•2y ago

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WillsterJohnsonOP•2y ago

yup that'd be it... apparently I was using 4.7 and forgot to add ^ to the version in package.json, thanks!

Unknown User•2y ago

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WillsterJohnsonOP•2y ago

this is just a toy project, I'm kinda expecting it to break often anyway. I tend to only use the basics of TS as well so hopefully they won't fundamentally change the language any time soon

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[TypeScript] correct way to tell typescript a property does exist?