What's the return type of a dynamic import?

Question

I have a file, which must be loaded asynchronously, so I made a function, which loads this file and returns the Promise:

export function load() {
    // ...
    return import(filename);
}

What is the return type of this Function? Promise<any> works, but it feels very weird. I'd like to write the signature as.

export function load() -> Promise<???>;

Answer 1

You need to use an import type and TypeScript 2.9 or higher. Here is an example:

my_module.ts

export const user = { name: "John", age: 30 };
export const event = { name: "Birthday", date: new Date(1989, 13, 2) };

demo.ts

type ModuleType = typeof import("./my_module"); // This is the import type!

export function load(): Promise<ModuleType> {
    // ...
    return import("./my_module");
}

(async () => {
    const module = await load();
    console.log(module.user.age); // It works!
})();

tsconfig.json (Added for reference)

{
  "compilerOptions": {
    "target": "es5",
    "module": "commonjs",
    "lib": [
      "es2015",
      "dom"
    ], 
    "strict": true,  
    "esModuleInterop": true
  }
}