How to create a Type from an Array of Strings and Objects

1. Arrays of objects

It can be useful to get a type from an array of values so that you can use it as

Let’s take this simple, although contrived, example using const assertions:

We will use const assertions (TypeScript 3.4+) to remove the duplication.

const sample_array= ["apple", "cat", "animal"] as const

// const sample_array: readonly ["apple", "cat", "animal"]

Getting a type from our array

Now we can get a type from our animals array using typeof:

const sample_array = ["apple", "cat", "animal"] as const;

type ICustomType = typeof sample_array[number]

// type ICustomType = 'apple' | 'cat' | 'animal'

2. Arrays of objects

const sample_array = [
  { year: 2021, value: 'The Little Things' },
  { year: 2022, value: 'Avatar: The Way of Water' },
  { year: 2023, movie: 'A Quiet Place: Day One' }
] as const
type ICustomType = typeof sample_array[number]['year']


// type ICustomType = 2021 | 2022 | 2023