Feature flags with a typed registry

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                  export const Flags = {
  NEW_EDITOR: 'new_editor',
  FAST_SEARCH: 'fast_search',
  BILLING_V2: 'billing_v2'
} as const;

export type FlagKey = typeof Flags[keyof typeof Flags];

export function isEnabled(flag: FlagKey, ctx: { userId?: string; percent?: number }) {
  if (ctx.percent == null) return false;
  // naive rollout example
  return (hash(flag + (ctx.userId ?? 'anon')) % 100) < ctx.percent;
}

function hash(s: string) {
  let h = 0;
  for (let i = 0; i < s.length; i++) h = (h * 31 + s.charCodeAt(i)) | 0;
  return Math.abs(h);
}

Ad-hoc feature flags turn into a mess of magic strings faster than most teams expect. I keep a typed registry so flags are discoverable and refactor-safe, and I resolve them centrally (user/org/rollout percentage) instead of scattering logic across components. On the frontend, I put the evaluation result in a context so UI code can gate behavior without doing its own network calls. The key is discipline: components should ask something like isEnabled(Flags.NEW_EDITOR) and not know why it’s enabled. I also treat flags as kill-switches—something you can disable quickly without redeploying. Used this way, flags are a safety tool, not permanent tech debt.

Mateo Rodriguez

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Feature flags with a typed registry

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