Theo's Typesafe Cult•4y 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•4y ago

Message Not Public

kliyerOP•4y ago

Thanks, that's exactly what I needed!

clover•4y ago

is that normal in your line of work

kliyerOP•4y 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

clover•4y ago

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

kliyerOP•4y ago

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

clover•4y ago

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

kliyerOP•4y 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•4y ago

Message Not Public

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Functions type for key of objects with specific key

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