在 TypeScript 声明中导入 JSON 文件（*.d.ts 文件）

Question

I am writing a declaration file which should declare a global type and strict to a specific list of string phrases.
These string phrases are actually part of property keys in an object located in a JSON file.

Two questions:

1. Is it possible to import a JSON file to a declaration file and process it using basic functions, like Object.keys and Array.map ?
2. Yet, I wonder, if it is even possible to use JS array of strings to define a type in TS?

Let me give you a code example.

Let's say we have the following JSON file named data.json :

{
  "someList": {
    "#key1": {"a": 1, "b": 2},
    "#key2": "some value",
    "#key3": 1234
  }
}

Now, I want to create the following declaration file global.d.ts :

import data from './data.json';

declare global {
  type AllowedKeys = Object(data.someList).map(key => key.substr(1));
}

Basically, I need the type to be defined (dynamically as JSON file changes) like this:

type AllowedKeys = "key1" | "key2" | "key3";

Any help or at least guidance would be appreciated.

Answer 1

You can have typescript infer a type from data in a json-file.

import data from "./data.json";


export type AllowedKeys = keyof typeof data["someList"];
// This is equivalent to
// export type AllowedKeys = "#key1" | "#key2" | "#key3"

The resulting d.ts file looks like this:

import data from "./data.json";
export declare type AllowedKeys = keyof typeof data["someList"];

As far as I know, there's no way to manipulate string literals in typescript (ie, removing the # ).

See those github issues:

• https://github.com/microsoft/TypeScript/issues/12940
• https://github.com/microsoft/TypeScript/issues/12754