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Mon, Oct 26

Sarah Thorne @sarah_ts 1w snippet 62c65d9

Zero-runtime deep immutable patch utility in TypeScript 5.4

Zero-runtime deep immutable patch utility in TypeScript 5.4. Preserves discriminated unions without pulling in Immer or Lodash — 12 lines, no dependencies.

immutable-patch.ts

type DeepPatch<T> = {
  [K in keyof T]?: T[K] extends object ? DeepPatch<T[K]> : T[K];
};

export const immutablePatch = <T extends object>(base: T, patch: DeepPatch<T>): T => ({
  ...base,
  ...Object.fromEntries(
    Object.entries(patch).map(([k, v]) =>
      [k, typeof v === 'object' && v !== null ? immutablePatch(base[k], v as any) : v]
    )
  ),
});

#TypeScript #DX

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ST Sarah Thorne @sarah_ts · 1 post

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