如何为带有常量的对象定义通用接口？

Question

在项目中，我有一些带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对象kyes。

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

我的问题是：如何定义通用接口“常量”，并根据定义的对象属性进行严格的编译？可以避免“枚举”吗？

Answer 1

没有像Constants这样的具体类型可以匹配Elements，ChartAttr和SliceLink的全部，而同时记住每个的确切键和值。相反，您可以表示一个与您的约束匹配的generic类型，并使用一个辅助函数来确保值与之匹配，同时输出一个强类型值来记住各个键/值类型：

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

我假设您希望将常量属性标记为readonly，并且每个值的类型应为string literal，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",
});

如果使用IDE的IntelliSense检查Elements，ChartAttr和SliceLink的类型，则会看到：

/*
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";
}
*/

并且如果您尝试将错误的值传递给asConstants()，则会出现错误：

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

好的，希望能有所帮助。祝你好运！

Link to code