Theo's Typesafe Cult•2y ago

Functions type for key of objects with specific key

Hey, are there any typescript wizards here that could help? I've been trying for a while already but don't really get there. I would like to type a function that takes in two arguments: an arbitrary object as the first argument and for the second argument a key of that object but only allow keys with e.g. a number as an associated value. What's the best way to do this? This is what I have so far. I only want to allow valueKeys which have a type number as a value. Thanks!

const BarChart = <
  T extends { date: Date },
  K1 extends keyof T,
>({
  data,
  valueKey,
}: {
  data: T[]
  valueKey: K1
}) => {...}

const BarChart = <
  T extends { date: Date },
  K1 extends keyof T,
>({
  data,
  valueKey,
}: {
  data: T[]
  valueKey: K1
}) => {...}

9 Replies

Unknown User•2y ago

Message Not Public

kliyer•2y ago

Thanks, that's exactly what I needed!

☘•2y ago

is that normal in your line of work

kliyer•2y ago

Haha I just love my typesafety. I'm just trying to get better at typescript which is why I'm trying these challenges. This was actually for my own product

☘•2y ago

okay adding these types of types (pun) adds maintenance burdens when the args change

kliyer•2y ago

Can you give an example where that would be a problem?

☘•2y ago

if the function needs different types of inputs thus changing the typing that's what I meant

kliyer•2y ago

Would it be better to use an accessor function then? Basically I wanna be able to pass a list of objects as a dateset and specify a property of every object to be used for the y value in the chart. That y value has to be of type number

Unknown User•2y ago

Message Not Public

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Functions type for key of objects with specific key