@quentinadam/unreachable

A simple library to assert unreachable code paths.

unreachable is meant for exhaustive checks. At compile time, TypeScript only accepts calls where the value has been narrowed to never (no possible value left). If it is still reached at runtime, it throws an AssertionError.

Usage

import unreachable from '@quentinadam/unreachable';

function transform(value: number | string) {
  if (typeof value === 'number') {
    return value * 2;
  }
  if (typeof value === 'string') {
    return value.toUpperCase();
  }
  return unreachable(value);
}