Type-Safe Feature Flags with TypeScript

Every flag used to be a magic string. Inevitably someone checked "new_checkout" against a flag named "new-checkout" and shipped a no-op.

A typed registry

const FLAGS = {
  newCheckout: { default: false },
  betaSearch: { default: false },
} as const;
 
type FlagName = keyof typeof FLAGS;
 
function useFlag(name: FlagName): boolean {
  // name is now autocompleted and typo-proof
  return resolve(name) ?? FLAGS[name].default;
}

Now useFlag("new_checkout") is a red squiggle, not a production incident. The whole abstraction is fifteen lines and pays for itself the first week.