How do I keep a literal union and the array or object used at runtime from drifting apart?

The recipe

const roles = ['admin', 'editor', 'viewer'] as const
type Role = (typeof roles)[number]

const routes = {
  home: '/',
  settings: '/settings',
} as const

type RouteName = keyof typeof routes
type RoutePath = (typeof routes)[RouteName]

The build compiles this and checks each result below.

How it works

1. 01

   const roles = ['admin', 'editor', 'viewer'] as const

   The const assertion preserves each element as a literal and makes the tuple readonly.

2. 02

   type Role = (typeof roles)[number]

   `typeof` captures the tuple and `[number]` collects every possible element.

What you get

• Role

  →"admin" | "editor" | "viewer"

• RouteName

  →"home" | "settings"

• RoutePath

  →"/" | "/settings"

Where it goes wrong

`as const` does not freeze the runtime object. It narrows the static view, so external or mutable data still needs validation and possibly an actual freeze.