How to define that a variable can only be a key attribute in an array

Question

How to dynamically obtain the type of key attribute in an array

const arr = [
  { key: 'a' },
  { key: 'b' },
  { key: 'c' },
];

type key = ??? // key is 'a' or 'b' or 'c'

CertainPerformance · Accepted Answer · 2022-06-09 03:37:25Z

2

Type the array as const so the strings don't get widened, and then you can use [number] on the array type to get a union of the objects, and then ['key'] on that to get a union of the strings.

const arr = [
  { key: 'a' },
  { key: 'b' },
  { key: 'c' },
] as const;

type key = typeof arr[number]['key'];

answered Jun 9, 2022 at 3:37

CertainPerformance

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