Computed import types

Suggestion

🔍 Search Terms

import label:feature-request

✅ Viability Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, new syntax sugar for JS, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

⭐ Suggestion

Add ability to typeof import() a string literal type

📃 Motivating Example

declare module 'test' {
    export const test: number;
}

type GetExport<T extends string> = typeof import(T)

type Test = GetExport<'test'> // typeof import('test') ≈ {test: number}

💻 Use Cases

babel, eslint and webpack use package names in their API, dynamically require them and proxy data into their interface. Generally, API that looks like

doSomething({
    package: 'package-name',
    options: {
        optionForThisPackage: 'value',
    },
});

could greatly improve on typing with this.

Also it's often the case with dynamic imports that resulting Promise gets passed through several other methods (like React.lazy or loadable from @loadable/component). Currently the only way to get good types there is to have these duplicated at every import() site. It would be possible to assign some types to wrapper function in this case too.

type LazyRegistry<Packages extends Record<string, string>> = {
    [Name in keyof Packages]: Promise<(typeof import(Name))[Packages[Name]]>
}
const lazyRegistry = <Packages extends Record<string, string>>(packages: Packages): LazyRegistry<Packages> => {
    return Object.fromEntries(
        Object.entries(packages).map(([name, importName]) => {
            const lazy = React.lazy(async () => {
                return (await import(name))[importName];
            });
            return [key, lazy] as const;
        }),
    ) as LazyRegistry<Packages>;
};

type LoadableRegistry<Packages extends Record<string, string>> = {
    [Name in keyof Packages]: AsLoadableComponent<typeof import(Packages[Name])>
}
const loadableRegistry = <Packages extends Record<string, string>>(packages: Packages) => {
    return Object.fromEntries(
        Object.entries(packages).map(([name, importName]) => {
            return [key, loadable(() => import(importName))] as const;
        }),
    ) as LoadableRegistry<Packages>;
};

const DynamicComponentRegistry = someRegistry({
    Foo: 'Foo',
    Bar: 'Bar',
});

Start by reviewing the existing handling of typeof import('literal') and the type-query examples in the issue. Define completion as allowing a generic string-literal type in typeof import(T) while preserving the demonstrated module and dynamic-import typing use cases; the payload names no repository files or tests.