type-dry.ts

// type from list of valid string values
type Category = 'action' | 'comedy' | 'drama'

// simple assignment (with IDE auto-complete)
const myCategory: Category = 'comedy'

const chooseCategory = () => {
  // BAD: repeat the list of categories for selection
  const categories = ['action', 'comedy', 'drama']
  return categories[1]
}

// --- SOLUTION: DRY (don't repeat yourself)
const categories2 = <const>['action', 'comedy', 'drama']
type Category2 = typeof categories2[number]

// simple assignment (with IDE auto-complete)
const myCategory2: Category2 = 'comedy'

// GOOD: list of valid strings not repeated. used as both values and type definition
const chooseCategory2 = () => categories2[1]