Typescript 接口特定键不同于索引

Question

I have an object with nearly all strings, except a few keys (which are known) which are string[] .

Interface MostlyStrings{
   [key:string]:string,
   specificKey1:string[],
   specificKey2:string[],
}

This does not work because string[] does not match the index.

I want to avoid [key:string]:string|string[] because then I will have to specify between string and array in all code.

Is it possible to interface that everything except a few known keys is a string ?

Answer 1

There's an open issue on the TS repo that's been tracking this for the past few years. Currently, it's not possible to do this.

You can achieve a similar effect by using an intersection type:

type MostlyStrings = {
   [key: string]: string;
} & {
   specificKey1: string[];
   specificKey2: string[];
};

You won't be able to construct an object literal of this type, but it will at least type-check/autocomplete correctly. In practice, you'll just need to do what you did in your example and update the index signature to include the types of the known properties as well, even though it doesn't accurately reflect your intention.