无法使用 Typescript (TS) 中的键访问对象值

Question

我有一个像这样的简单对象：

export const daysOfTheWeek = {
  0: "Sunday",
  1: "Monday",
  2: "Tuesday",
  3: "Wednesday",
  4: "Thursday",
  5: "Friday",
  6: "Saturday",
};

我正在尝试使用像这样的变量来访问它：

const checkDay = (dayIndex: number):void => {
  console.log(daysOfTheWeek[dayIndex]) // error happens here
};

我希望记录 "Sunday"，但是我收到不断弹出的错误：

Element implicitly has an 'any' type because expression of type 'number' can't be used to index type '{ 0: string; 1: string; 2: string; 3: string; 4: string; 5: string; 6: string; }'.
  No index signature with a parameter of type 'number' was found on type '{ 0: string; 1: string; 2: string; 3: string; 4: string; 5: string; 6: string; }'.ts(7053)

关于如何解决这个问题有什么建议吗？

Answer 1

您需要告诉 TypeScript dayIndex: number 实际上不仅仅是一个数字，而是 daysOfTheWeek 键之一。

const checkDay = (dayIndex: keyof typeof daysOfTheWeek):void => {
  console.log(daysOfTheWeek[dayIndex])
};

如果你做不到，那么你必须在函数内部缩小范围

const checkDay = (dayIndex: number):void => {
  if (dayIndex !== 1 && dayIndex !== 2 ...) {
    throw new Error('Not a day of the week');
  }
  console.log(daysOfTheWeek[dayIndex])
};

或在检查范围后声明它：

const checkDay = (dayIndex: number):void => {
  if (!Number.isInteger(dayIndex) || dayIndex < 0 || dayIndex > 6) {
    throw new Error('Not a day of the week');
  }
  console.log(daysOfTheWeek[dayIndex as keyof typeof daysOfTheWeek])
};

无法使用 Typescript (TS) 中的键访问对象值

Can't access object values using keys in Typescript (TS )

types

object

typescript