TypeScript magic with Extract

extract.ts

// source: https://twitter.com/mpocock1/status/1385610014639988739

const fields = [{
  inputType: 'text',
  label: 'ID',
  name: 'id'
}, {
  inputType: 'text',
  label: 'Description',
  name: 'description'
}, {
  inputType: 'number',
  label: 'Price',
  name: 'price'
}] as const

type Field = (typeof fields)[number]

type Item = { [K in Field['name']]: Extract<Field, { name: K }> extends { inputType: 'number' } ? number : string }

const item: Item = {
  description: 'yeah',
  id: 'id',
  price: 12
}