TypeScript - how to decide if a value is of a type in runtime

Check is value is member of Union type

“Array first” approach
https://dev.to/hansott/how-to-check-if-string-is-member-of-union-type-1j4m

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const ALL_SUITS = ['hearts', 'diamonds', 'spades', 'clubs'] as const
type SuitTuple = typeof ALL_SUITS // type SuitTuple = readonly ["hearts", "diamonds", "spades", "clubs"]
type Suit = SuitTuple[number] // type Suit = "hearts" | "diamonds" | "spades" | "clubs"

Type guard function

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function isSuit(value: string): value is Suit {
  return ALL_SUITS.includes(value as Suit)
}