receive types from a array of objects value

Question

i want to generate types out from a array of objects.

const names = [
  {
    name: 'Bob'
  },
  {
    name: 'Jane'
  },
  {
    name: 'John'
  },
  {
    name: 'Mike'
  },
]

the result should be look like this:

type NameType = 'Bob' | 'Jane' | 'John' | 'Mike'

i saw a lot of references, for example this typescript-types-from-arrays

but these examples always use a array of strings as resource. like:

const array = ['one', 'two',...]

which works flawless.

but what i try to do is generating the types with a array.map like this:

const allNames = names.map((item) => item.name) as const;

type NameType = typeof names[number];

but this leads into a:

A 'const' assertions can only be applied to references to
enum members, or string, number, boolean, array, or object literals.

here is a playable example of what i try to do: Stackblitz

i want to use the function getName() with IntelliSense to know which names are available in the names array. like this:

nate-kumar · Accepted Answer · 2022-11-26 10:23:54Z

4

This can be still achieved using a combination of as const and indexed access types

const names = [
  {
    name: 'Bob'
  },
  {
    name: 'Jane'
  },
  {
    name: 'John'
  },
  {
    name: 'Mike'
  },
] as const

type NameType = typeof names[number]['name'];
// type NameType = "Bob" | "Jane" | "John" | "Mike"

TypeScript Playground

answered Nov 26, 2022 at 10:23

nate-kumar

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