R
roblox-ts•3y ago
PoppingPopper

Conditional Return Type

I have a question. Let's say, I want to create a function that takes in 1 optional parameter arg of type T. The function also returns the value of the optional parameter. 
function foo<T>(arg?: T) {
  return arg
}
function foo<T>(arg?: T) {
  return arg
}
In this scenario, is it possible for me to affect the return type to where it would return the value as T or as T | undefined based on whether or not arg is provided? 
const test1 = foo<string>() //typeof test1 === string | undefined
const test2 = foo('string') //typeof test2 === string
const test1 = foo<string>() //typeof test1 === string | undefined
const test2 = foo('string') //typeof test2 === string
LOL forgot about function overloading... Nevermind.
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