TypeScript对象类型断言不工作

Question

type ConfigItem<T> = {
  label: string;
  name: keyof T;
};

type P1 = {
  E1: {
    A: "xl",
    B: "xl",
    C: "xl",
    D: "xl",
  },
  E2: {
    AA: "xxl",
    BB: "xxl",
    CC: "xxl",
    DD: "xxl",
  },
};

export const Configs = {
  X1: [
    { label: "ax", name: "A2" }, // ⬅️ Why is it not restricted?
    { label: "bx", name: "B" },
    { label: "cx", name: "C" },
    { label: "dx", name: "D2" }, // If the last one is not in E1, an error is reported.
  ] as ConfigItem<P1["E1"]>[],
  X2: [
    // ...
  ]
};

只有当数组中的最后一项具有错误的值类型时，才会报告错误。

当最后一项正确时，前一项不正确，则不会报告错误。

"typescript": "^4.4.4"

更新：是唯一的方法吗？

const X1: ConfigItem<P1["E1"]> = [
  { label: "ax", name: "A2" },
  { label: "bx", name: "B" },
  { label: "cx", name: "C" },
  { label: "dx", name: "D" },
];

export const Configs = {
  X1,
  X2: []
};

Answer 1

当您使用as [[typename]]符号时，不会执行类型检查，因为您正在手动告诉编译器，您确信这是正确的。

要启用类型检查，您要做的是：

type ConfigItem<T> = {
  label: string;
  name: keyof T;
};

type P1 = {
  E1: {
    A: "xl",
    B: "xl",
    C: "xl",
    D: "xl",
  },
  E2: {
    AA: "xxl",
    BB: "xxl",
    CC: "xxl",
    DD: "xxl",
  },
};

export const Configs: {X1: ConfigItem<P1["E1"]>[], X2: any /*define next here*/} = {
  X1: [
    { label: "ax", name: "A2" },
    { label: "bx", name: "B" },
    { label: "cx", name: "C" },
    { label: "dx", name: "D2" },
  ],
  X2: [
    // ...
  ]
};