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useGroupedTypeImport (since v1.0.0)

Diagnostic Category: lint/nursery/useGroupedTypeImport

Source: no-import-type-side-effects

Enforce the use of import type when an import only has specifiers with type qualifier.

The --verbatimModuleSyntax TypeScript’s compiler option causes TypeScript to do simple and predictable transpilation on import declarations. Namely, it completely removes import type and any imported names with the type qualifier.

For instance, the following code:

import { type A, type B } from "mod-1";
import type { C, D } from "mod-2";
nursery/useGroupedTypeImport.js:1:8 lint/nursery/useGroupedTypeImport  FIXABLE  ━━━━━━━━━━━━━━━━━━━━

  ✖ The type qualifier can be moved just after import to completely remove the import at compile time.
  
  > 1 │ import { type A, type B } from "mod-1";
      │        ^^^^^^^^^^^^^^^^^^
    2 │ import type { C, D } from "mod-2";
    3 │ 
  
  ℹ Only import type are removed at compile time.
  
  ℹ Unsafe fix: Use import type instead.
  
    1   │ - import·{·type·A,·type·B·}·from·"mod-1";
      1 │ + import·type·{·A,·B·}·from·"mod-1";
    2 2 │   import type { C, D } from "mod-2";
    3 3 │

is transpiled to:

import "mod-1";

Note that, an import that includes only names qualified with type is transpiled to a side-effect import. This can be a surprising behavior: most of developers could expect the deletion of the import.

This behavior may still be desirable for applying the potential side-effects of the imported module. In most cases you will not want to leave behind an unnecessary side effect import. In teh remaining cases, it is often preferable to explicitly use a side-effect import to apply the side-effects of a module:

import "mod"; // side-effect import
import type { A, B } from "mod";

Examples

Section titled Examples

Invalid

Section titled Invalid
import { type A } from "mod";
nursery/useGroupedTypeImport.js:1:8 lint/nursery/useGroupedTypeImport  FIXABLE  ━━━━━━━━━━━━━━━━━━━━

  ✖ The type qualifier can be moved just after import to completely remove the import at compile time.
  
  > 1 │ import { type A } from "mod";
      │        ^^^^^^^^^^
    2 │ 
  
  ℹ Only import type are removed at compile time.
  
  ℹ Unsafe fix: Use import type instead.
  
    1   │ - import·{·type·A·}·from·"mod";
      1 │ + import·type·{·A·}·from·"mod";
    2 2 │

Valid

Section titled Valid
import type { A, B } from "mod";
import { A, type B } from "mod";
Section titled Related links