@webframe/assert-unreachable

This package provides a utility function that throws an error if a code path is reached that should be unreachable. This is useful for catching logic errors in your code with typescript.

Installation

npm install @webframe/assert-unreachable // or
yarn add @webframe/assert-unreachable

Basic Example

import { assertUnreachable } from '@webframe/assert-unreachable';

const values = [
  'one',
  'two',
  'three',
] as const

for (const value of values) {
  switch (value) {
    case 'one':
      console.log('one');
      break;
    case 'two':
      console.log('two');
      break;
    case 'three':
      console.log('three');
      break;
    default:
      // Throws a typescript error if the switch statement is not exhaustive
      assertUnreachable(value);
  }
}

Usage

The assertUnreachable()'s first argument is the value that should be unreachable. The type of which should be never. If it is not never (i.e the switch statement is not exhaustive), typescript will throw an error.

The assertUnreachable()'s second argument is an optional message that is used for the error message.

const value = true

if (value === true) {
  return
}

assertUnreachable(value, 'This should never happen');