Export and import types

[nazarhussain]

Problem description

A discussion point raised during recent refactoring. Should we export/import types with the Typescript, which we currently don't.

That's our current use case.

// module.ts
type MyType = string | number;

export { MyType };

and for import

import {MyType} from "./module.js"

Solution description

TS recommends to use to type based export/import for types.

// module.ts
type MyType = string | number;

export { type MyType };

and for import

import type {MyType} from "./module.js"

This pattern have some advantages:

1. Bundlers and compilers other than TS can easily detect and remove the types from the compiled JS
2. Avoiding Unintentional Side Effects

This pattern have some disadvantages:

1. Use of extra type keyword for the types at time of import.
2. Split the exports of objects and types explicitly

Additional context

https://biomejs.dev/linter/rules/use-export-type
https://biomejs.dev/linter/rules/use-import-type

[nflaig]

import type {MyType} from "./module.js"

this makes sense if you only import types from the file / module, this will completely remove it from dist

[philknows]

We agree that we should do both of these things. And enforce them with linter rules.