Function assertExhaustive

assertExhaustive(_: never, error?: string | Error): never

Assert that this line is unreachable, useful for exhaustive checks such as a switch covering every case of a union.

Parameters

_: never
error: string | Error = 'Failed exhaustive check'

Returns never

Example

type Direction = 'up' | 'down';

function describe(direction: Direction): string {
  switch (direction) {
    case 'up':
      return 'Going up';
    case 'down':
      return 'Going down';
    default:
      assertExhaustive(direction); // throws if a new Direction case isn't handled above
  }
}