allow local module type declarations on separate files (similar to C .h files)

Search Terms

.d.ts definitions ambient module typing local

Suggestion

I would like to being able to compose typescript modules/components inside my application .i.e. src/components/Foo.ts and being able to declare its typings under src/components/Foo.d.ts where typescript would either infer those types automatically.

Disclaimer: It may happen that this is already possible, but I already researched everywhere and read the documentation as well as trying to declare ambient modules (which won't work with relative paths), so I am trying this as a last resort in case it's indeed not currently possible.

Use Cases

Sometimes, when creating components inside an application, some may have a quite extensive type set which usually makes the file difficult to read and take the focus away from the implementation.
Like so:

src/component/Foo.ts
##########################
#         type           #
#         type           #
#         type           #
#         type           #
#         type           #
#                        #
#    implementation      #
#    implementation      #
##########################

This would make it easier for the developer to organise their code similar to C's .h files separating the definition from implementation.

Examples

Project structure:

src/components
src/components/Foo.ts
src/components/Foo.d.ts
src/components/complex/index.ts
src/components/complets/index.d.ts

types are automatically inferred within the main module

src/components/Foo.ts

const bar:Bar = {foo:1,bar:2};
export default ...

src/components/Foo.d.ts

type Bar = {foo:number; bar:number; }
export type ExportedType = string[];

types can still be imported from a different component

src/components/Bar.ts

import type {ExportedType} from './Foo';
import type {Bar} from './Foo'; // < Error as Bar is not exported

This would result in:

src/component/Foo.d.ts                    src/components/Foo.ts
##########################                ##########################
#         type           #                #    implementation      #
#         type           #                #    implementation      #
#         type           #                #                        #
#         type           #                #                        #                        
#         type           #                #                        #
##########################                ##########################

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, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

Verwende das vorgeschlagene Beispiel mit src/components/Foo.ts und src/components/Foo.d.ts als Ausgangspunkt für die Reproduktion, einschließlich der in src/components/Bar.ts gezeigten Imports. Untersuche zunächst, wie TypeScript derzeit Deklarationen für ein relatives Modul auflöst, und ermittle dann die erwartete Sichtbarkeit von Bar und ExportedType. Als abgeschlossen gilt die Aufgabe, wenn die separate Deklarationsdatei mit Foo.ts verknüpft ist und dabei das angegebene Exportverhalten erhalten bleibt.