如何用常量定义Object的通用接口

Question

在项目中，我有几个具有字符串常量的对象。例如：

export const Elements: Constants {
DESCRIPTION: "DescriptionAutoField2",
FORMULA_CALC: "FormulaCalcAutoField1",
CHART_CODE: "ChartCodeAutoField1",
CHART_CODE_DESCRIPTION: "ChartDescriptionAutoField1",
};
export const ChartAttr: Constants = {
CHART: "Chart",
CHART_DESCRIPTION: "ChartDescr",
};
export const SliceLink: Constants = {
SLICE_CODE: "SliceCode",
SLICE_DESC: "SliceDesc",
SLICE_CALC: "SliceCalc",
};

我这样定义了接口，但在这种情况下，无法在编译期间检查Object kyes。

export interface Constants {
[key: string]: string;
}

我的问题是：如何定义通用接口"常量"，并根据定义的Object属性进行严格编译？是否可以避免"枚举"？

Answer 1

没有像Constants这样的单一具体类型可以匹配所有Elements、ChartAttr和SliceLink，而同时记住每个类型的确切键和值。相反，您可以表示一个与约束匹配的泛型类型，并使用辅助函数来确保值符合约束，同时输出一个记住单个键/值类型的强类型值：

// helper function
const asConstants = <S extends string, T extends Record<keyof T, S>>(
c: T
): { readonly [K in keyof T]: T[K] } => c;

我假设您希望常量属性标记为readonly，并且每个值的类型应该是字符串文字，而不仅仅是string。

现在，您可以通过函数而不是注释来定义常量：

export const Elements = asConstants({
DESCRIPTION: "DescriptionAutoField2",
FORMULA_CALC: "FormulaCalcAutoField1",
CHART_CODE: "ChartCodeAutoField1",
CHART_CODE_DESCRIPTION: "ChartDescriptionAutoField1",
});
export const ChartAttr = asConstants({
CHART: "Chart",
CHART_DESCRIPTION: "ChartDescr",
});
export const SliceLink = asConstants({
SLICE_CODE: "SliceCode",
SLICE_DESC: "SliceDesc",
SLICE_CALC: "SliceCalc",
});

如果您使用IDE的IntelliSense检查Elements、ChartAttr和SliceLink的类型，您会看到：

/*
const Elements: {
readonly DESCRIPTION: "DescriptionAutoField2";
readonly FORMULA_CALC: "FormulaCalcAutoField1";
readonly CHART_CODE: "ChartCodeAutoField1";
readonly CHART_CODE_DESCRIPTION: "ChartDescriptionAutoField1";
}
const ChartAttr: {
readonly CHART: "Chart";
readonly CHART_DESCRIPTION: "ChartDescr";
}
const SliceLink: {
readonly SLICE_CODE: "SliceCode";
readonly SLICE_DESC: "SliceDesc";
readonly SLICE_CALC: "SliceCalc";
}
*/

如果你试图将一个坏值传递给asConstants()，你会得到一个错误：

asConstants({
NOT_A_STRING: 1, // error! number not a string        
})

好吧，希望能有所帮助。祝你好运

链接到代码