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    Function objectExtendEach

    • Like objectMap, but preserves the per-key correlation between each original value's type and the result by extending every value with the same additional properties rather than mapping it to an unrelated type. Phrasing the result as { [K in keyof O]: O[K] & Ex } in the return type evaluates O[K] fresh per key, where a single generic R would collapse to a union.

      Type Parameters

      • O extends Record<string, any>
      • Ex extends Record<string, unknown>

      Parameters

      • original: O
      • extendFn: (value: O[keyof O & string], key: string & keyof O) => Ex

      Returns { [K in string | number | symbol]: O[K] & Ex }

      const chains = {
        ethereum: { namespace: 'eip155', reference: '1' },
        solana: { namespace: 'solana', reference: 'mainnet' },
      } as const;

      const withChainId = objectExtendEach(chains, v => ({
        chainId: `${v.namespace}:${v.reference}`,
      }));
      // {
      //   ethereum: { namespace: 'eip155'; reference: '1' } & { chainId: string };
      //   solana:   { namespace: 'solana'; reference: 'mainnet' } & { chainId: string };
      // }

      Each value in original must be an object, because the implementation spreads v ({ ...v, ...extendFn(v, k) }) — spreading a primitive would silently yield an empty object (or, for strings, per-character indices) and the intersection O[K] & Ex would collapse to never for primitive O[K]. Constraining O to Record<string, object> makes the type and runtime behavior agree.

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