Add `import type "mod"`

Search Terms

type-only import

Suggestion

The new type-only import syntax supports most variations of import statement but not this one:
import type 'mod'
It may seem stupid because no type is actually imported?! But it's in fact useful if mod contains some global declarations that you need.

Global declarations are currently only imported from: typeroots (@types/* by default) or types configs; and referenced modules.

This syntax is even more useful because it can't be emulated today. If you do import 'mod' then typing works but TS assumes you import the module for side-effects and will not erase it.(EDIT: see triple-slash comment)

Use Cases

I encountered this today.
One package I use provides some dependency injection and basically defines the following module augmentation:
inject(x: 'myType'): MyType
which is a strongly typed overload of
inject<T = unknown>(x: string): T.
Inject itself comes from another library so code that wants to use this import needs to do this:

import { inject } from 'other-lib';
import type 'my-lib';

let my = inject('myType'); // correctly typed as MyType

Current work-arounds include:

• Importing a type import { MyType } from 'my-lib' but if you don't use it in code it'll be a warning;
• Import without type import 'my-lib' but it won't be erased;
• Add this lib to typeroots or types and do nothing (might be better in some cases). (EDIT: not really working, see my comment below for an alternative solution.)
• Use /// <reference types="mod" />, which works but I think most people have forgotten about? (I have 😜)

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.

この issue では、実行時の出力を発生させずにグローバル宣言を読み込むための import type "mod" のサポートを提案しており、モジュール拡張を伴う例が示されています。issue では実装ファイルやテストが特定されていないため、まず import パーサー、型チェック、emit のテストを見つけてください。構文が型チェックを通過し、意図した消去済みの出力を生成すれば完了です。