babel-loader: Typescript: Unable to re-export a type with Webpack 4

I’m submitting a bug report Webpack Version: 4.4.1 Babel Core Version: 7.0.0-beta.44 Babel Loader Version: 8.0.0-beta.0 Please tell us about your environment:

I am using Bable beta with the typescript preset.

In one file, I define and export a type:

// a.ts
export type MyType = "a" | "b";

In another file, I re-export this type:

// b.ts
export { MyType } from "./a.ts";

Current behavior:

The export line is not present when a.ts is compiled using Babel. The re-export line in b.ts is compiled to:

export { MyType } from "./b";

Webpack fails with this error:

    ERROR in ./app/client/utils.ts
    79:0-51 "export 'myType' was not found in './a'
     @ ./b.ts

Expected/desired behavior:

It worked fine with Webpack 3, I am not sure why. babel should not output anything for the re-export but it does. I am not sure why Webpack 3 was not complaining about the issue, but now Webpack 4 does.

I am not sure if this should be filled in this repo, or with Webpack or Babel core. I can provide a repro if this is needed and the correct place for this issue.

About this issue

Original URL
State: closed
Created 6 years ago
Reactions: 23
Comments: 17 (3 by maintainers)

Links to this issue

Most upvoted comments

You can still do are-export if it’s clear that you’re exporting a type:

import { T as a_T } from "./a";
export type T = a_T;

You can also do export * from "./a";.

+35

ghost on Sep 4, 2018

@niksumeiko, that cool, but not supported by babel-loader; export type { IGeocoder } from './types'; crush build with Unexpected token error

+23

Akiyamka on Mar 20, 2020

This is also a problem you would encounter with ts-loader if you were using the --isolatedModules option, which emits code without knowledge of the types of other modules (types only used for checking, not emit).

The babel typescript transform works pretty much just like tsc’s transform with --isolatedModules enabled.

Webpack 4 now complains about the error because this checking was added but disabled by default in webpack 3; it’s just enabled by default in webpack 4.

A way of reexporting that works on both babel and typescript --isolatedModules would be this:

import { MyType } from './a'
export type MyType = MyType

but tsservice doesn’t seem to treat the reexport the same as the original for purposes of go-to-definition and find usages.

+21

Jessidhia on Jun 22, 2018

export * from './a' seems to be working

+13

mkazlauskas on Jun 23, 2018

This issue will be fixed in Typescript 3.8. They already have a merged PR microsoft/TypeScript#35200 that will introduce import type, export type keywords.

A new syntax for type-only imports and exports will look as follows:

import type T from './mod';
import type { A, B } from './mod';
import type * as Types from './mod';
 
export type { T };
export type { T } from './mod';

https://devblogs.microsoft.com/typescript/announcing-typescript-3-8-beta/

+11

niksumeiko on Feb 7, 2020

The last comment here by @Akiyamka addresses an issue I’ve ran into lately. I still get an Unexpected token error. Is this syntax supported or not?

export type { IGeocoder } from './types';

petmat on Nov 12, 2020

@SapienTech to be more exact, to get this to work I had to specifically update to "@babel/preset-typescript": "^7.12.7",

iyobo on Dec 2, 2020

@donaldpipowitch I’ve also had success (at least with my config) with the following, no as needed:

import { T } from "./a";
export type T = T;

edit: I see this was already mentioned in an earlier comment, that’s probably where I got the idea 😃

ubnt-marc-khouri on Sep 4, 2018

@petmat I had same issue, and updating to latest babel fixed it for me.

dylanjeffers on Nov 30, 2020