Cannot 'export default' abstract, ambient class or interface

export default abstract class B {

}

By the way, the same with

export default declare class B {

}

Seems to be a parser bug

In what situations would one need to make an ambient class a default export?

These two are by desing. We have felt that the export default syntax is already long enough, so no modifiers are needed. for a workaround use:

declare class  C {}
export default C;

We should just allow these. It's a strange inconsistency, the workaround is more verbose, and the error gives you no help getting to the workaround.

Dan Quirk (@danquirk)

Yeah, discussed with Dan Quirk (@danquirk) and Ryan Cavanaugh (@RyanCavanaugh) offline; in a .d.ts file, a default exported ambient class makes sense.

I don't think it's that unreasonable to support the original syntax.

should also cover interfaces (#3914):

export default interface User {
    wpUserID: string;
}

And namespaces: export default namespace foo { ... } (#7407)

Accepting PRs for this.

Unsupported export default patterns:

export default abstract class C { } Added by Allow export default abstract class. Related to issue 3792. #14657
export default declare class C { }
export default interface I { } Added by Allow export default interface. Related to issue 3792. #16040
export default enum E { }
export default const enum E { }
export default namespace N { }
export default type T = { }

Mohamed Hegazy (@mhegazy)

Mohamed Hegazy (@mhegazy) what about export default type foo = {} ?

Mohamed Hegazy (@mhegazy)

Mohamed Hegazy (@mhegazy) for full symmetry with JS export forms, consider (strawman syntax) export default as ...:

JS	TS
`export const x = 123`	`export type T = number`
`export { x }`	`export { T }`
`export class Foo {}`	`export interface Foo {}`
`export default class Foo {}`	`export default interface Foo {}`
`export default 123`	`export default as number`

not sure what that means..

export default as number

but if it is a .d.ts, we chose not to have a special syntax for this, and the recommendation here is to use

declare cosnt _t: number;
export default _t;

Yeah, sorry, it is a bit ambiguous. Currently, you can sort of export a type as default with:

type T = number;
export default T;

By analogy of const ~= type:

export const x = 123;
export type T = number;
export default x;
export default T;
export default 123;
export default ???; // can't put type expressions here, only type names, due to ambiguity

The motivating case would would be something like:

// Action.ts
export default as
  | { type: 'login', name: string, password: string }
  | { type: 'logout' }
  | ...

where currently you would need to bury the export at the bottom of the file.

I picked export default as <type> as strawman simply because as already suggests a type on RHS, but it doesn't really imply the right thing, you're right. Perhaps export type default <type>?

Changed parser.ts to support all forms of export default described in m…

Adrian Leonhard (@NaridaL)

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Cannot 'export default' abstract, ambient class or interface #3792

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Cannot 'export default' abstract, ambient class or interface #3792

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DanielRosenwasser commented on Jul 9, 2015

mhegazy commented on Jul 9, 2015

danquirk commented on Jul 9, 2015

DanielRosenwasser commented on Jul 9, 2015

mhegazy commented on Feb 22, 2016

RyanCavanaugh commented on Mar 7, 2016

RyanCavanaugh commented on Mar 15, 2016

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mhegazy commented on May 23, 2017

anstarovoyt commented on Aug 15, 2017

simonbuchan commented on Jan 11, 2018

mhegazy commented on Jan 11, 2018

simonbuchan commented on Jan 11, 2018

alvis commented on Jan 30, 2018

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