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.

Issue đề xuất hỗ trợ import type "mod" để tải các khai báo toàn cục mà không phát sinh mã ở runtime, với một ví dụ liên quan đến module augmentation. Issue không xác định các tệp triển khai hoặc test, vì vậy trước tiên hãy tìm các test cho import parser, type-checking và emit; hoàn thành có nghĩa là cú pháp vượt qua type-checking và tạo ra output đã được loại bỏ như dự kiến.