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I would like to have a list of objects whose:

  • keys are unrestricted and unique for each object
  • values are string arrays

For example:

const obj1 = {
    'animals': ['cat', 'dog', 'mouse'],
    'fruits': ['apple', 'orange', 'strawberry', 'kiwi', 'grape']
}
const obj2 = {
    'name': ['Einstein', 'Hitler'],
    'country': ['Nigeria', 'Afganistan', 'Vietnam', 'Egypt']
}

How do I declare them?

Ooker
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  • you can do this by defining interface with an index signature that allow for unrestricted keys and enforces that the values are string arrays – Hasan Raza Jul 26 '23 at 06:17

1 Answers1

1

COnsider this approach:

interface A {
  [prop: string]: Lowercase<string>[]
}

const obj1: A = {
  'animals': ['Cat', 'dog', 'mouse'], // expected error
  'fruits': ['apple', 'orange', 'strawberry', 'kiwi', 'grape']
}

type B = Record<string, Capitalize<string>[]>

const obj2: B = {
  'name': ['Einstein', 'doe'], // expected error
  'country': ['Nigeria', 'Afganistan', 'Vietnam', 'Egypt']
}

Playground

Lowercase and Capitalize are string utility helpers to assure that each string value should match some pattern

Question: Why A is an interface and B is a type ?

Answer: There is a big difference between types and interfaces in terms of indexing. See my answer and my article. Use interface when you want to have more strict rules about object type shape.

captain-yossarian from Ukraine
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