我如何使這個 typescript function 返回強類型數組而不是 string[]

Question

我有這個 function，我正在嘗試將其從 js 轉換為 ts，我認為變量hi的類型將是('s'|'bb')[]但實際上它是string[] 。 我怎樣才能得到 typescript 來推斷 K 是 NewOptions 的鍵？

export const getWithOverrides = <
  K extends string,
  NewOptions extends { [x in K]?: boolean },
  Overrides extends { [x in K]?: boolean }
>(
  newOptions: NewOptions,
  overrides: Overrides
): K[] =>
  (Object.keys(newOptions) as K[]).filter(key => {
    if (typeof overrides[key] === 'boolean') {
      return overrides[key];
    }
    return newOptions[key];
  });

const hi = getWithOverrides({ s: true, bb: true }, { s: true });

Answer 1

您可以通過刪除K類型參數來做到這一點，要求 object 類型擴展Record<string, boolean> ，並將keyof與您的兩個 object 類型一起使用：

export const getWithOverrides = <
    NewOptions extends Record<string, boolean>,
    Overrides extends Record<string, boolean>
>(
    newOptions: NewOptions,
    overrides: Overrides
): (keyof NewOptions | keyof Overrides)[] =>
    Object.keys(newOptions).filter((key) => {
        if (typeof overrides[key] === "boolean") {
            return overrides[key];
        }
        return newOptions[key];
    });

const hi = getWithOverrides({ s: true, bb: true }, { s: true });
//    ^? const hi: ("s" | "bb")[]

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