Support importing types from a .mts file from within a CommonJS file. #58195
Description
🔍 Search Terms
"commonjs", "import", "type", "module"
✅ Viability Checklist
- 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 isn't a request to add a new utility type: https://github.com/microsoft/TypeScript/wiki/No-New-Utility-Types
- This feature would agree with the rest of our Design Goals: https://github.com/Microsoft/TypeScript/wiki/TypeScript-Design-Goals
⭐ Suggestion
Proposal: Allow importing pure types from .mts files from a CommonJS file.
The current behavior generates an unnecessary / incorrect error since no require will be emitted.
Current error:
Please note, future versions of Node will support requiring an ESM module if a there is not a top level await. See:
📃 Motivating Example
src/code.cts
import type { EntityId, Entity, User } from './models.mjs';
export function userName(user: User): string {
return user.name;
}src/models.mts
export type EntityId = string;
export interface Entity {
id: EntityId;
}
export interface User extends Entity {
name: string;
}💻 Use Cases
- What do you want to use this for?
In mixed code bases (especially as they transition from CommonJS to ESM) it is often necessary export the types from a module that are used in CommonJS files. - What shortcomings exist with current approaches?
All shared types must be declared in CommonJS files or inferred usingAwaited. - What workarounds are you using in the meantime?
Declaring shared types in CommonJS files.