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Discussion on: Understanding Generics in TypeScript

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Replies for: Hey Mike! Did you checkout the interactive tutorial? Maybe that would be helpful as well! To answer your question, let's say we used returnStringO...

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iam_danieljohns profile image
Daniel Johns •

I tried this and it still ran. Is this just a JS issue or am I missing something?

function returnStringOrNumber<T>(arg: T): T {
  return arg
}
let value = returnStringOrNumber<number>(123) + "hello"
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plondon profile image
Philip London •

Hey @iam_danieljohns that's perfectly valid JavaScript, in this case value will be cast to a string type because concatenating a number and a string results in a string. In this case value will be "123hello".

If you wanted to make sure that value was indeed a number type you could do:

let value: number = returnStringOrNumber<number>(123) + "hello"
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