javascript - 如何在 TypeScript 界面中强制键类型？

Question

我想创建一个对象接口(interface)，强制使用字符串作为键，但 TypeScript 编译器传递代码，即使它有数字类型作为键。为什么？

例如，

interface PriceI {
    [key:string]:number;
}

var coursePrice: PriceI = {};
coursePrice["Orange"] = 100;
coursePrice["Apple"] = 200;
coursePrice[3]=200;    // It should be compile error, but it pass
coursePrice[true]=300; // It's compile error

Answer 1

参见the handbook :

There are two types of supported index signatures: string and number. It is possible to support both types of indexers, but the type returned from a numeric indexer must be a subtype of the type returned from the string indexer. This is because when indexing with a number, JavaScript will actually convert that to a string before indexing into an object. That means that indexing with 100 (a number) is the same thing as indexing with "100" (a string), so the two need to be consistent.

在您的示例中，TypeScript 认为 coursePrice[3] = 200; 相当于 coursePrice["3"] = 200;。