Define interface by an array of values

Question

If I have a constant with input props and a function that returns the input ids and its default value, like this:

const Inputs = [{label: "myInput1", id: "myId1"}, {label: "myInput2" , id: "myId2" }]
    
const getInputValues = () => Inputs.reduce( (acc, item) => ({...acc, [item.id] : 123  }), {} )

How can I define the return type of getInputValues in TypeScript?

Code

I don't want to use any. There is no way to do it without any? — Braven
– Braven, Commented Sep 28, 2020 at 16:40
Did you tried making an interface as your question title displays ? — Wasim
– Wasim, Commented Sep 28, 2020 at 16:46

gurisko · Accepted Answer · 2020-09-28 17:04:41Z

3

The only way I could think of is to use const assertion for your Inputs constant:

const Inputs = [
  {label: "myInput1", id: "myId1"},
  {label: "myInput2", id: "myId2"},
] as const;

type InputIds = typeof Inputs[number]['id'];

function getInputValues(): Record<InputIds, number> {
  return Inputs.reduce((acc, item) => {
    return {...acc, [item.id]: 123};
  }, {} as Partial<Record<InputIds, number>>) as Record<InputIds, number>;
}

edited Sep 28, 2020 at 17:04

answered Sep 28, 2020 at 17:00

gurisko

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2 Comments

Titian Cernicova-Dragomir Over a year ago

{[K in InputIds]: number} can be replaced with Record<InputIds, number>,

gurisko Over a year ago

@TitianCernicova-Dragomir Thank you! Definitely more readable. I edited my answer.

spender · Accepted Answer · 2020-09-28 17:05:19Z

1

The best you can hope for here is Record<string, number>.

const getInputValues = ():Record<string,number> => 
    Inputs.reduce( (acc, item) => ({...acc, [item.id] : 123  }), {})

For even better type-safety, you might choose Record<string, number | undefined> which will force you to type-check any values you access.

edited Sep 28, 2020 at 17:05

answered Sep 28, 2020 at 16:44

spender

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