typescript/no-import-type-side-effects Restriction

🛠️ An auto-fix is available for this rule.

What it does

Enforce the use of top-level import type qualifier when an import only has specifiers with inline type qualifiers.

Why is this bad?

The --verbatimModuleSyntax compiler option causes TypeScript to do simple and predictable transpilation on import declarations. Namely, it completely removes import declarations with a top-level type qualifier, and it removes any import specifiers with an inline type qualifier.

The latter behavior does have one potentially surprising effect in that in certain cases TS can leave behind a "side effect" import at runtime:

import { type A, type B } from "mod";

is transpiled to

import {} from "mod";
// which is the same as
import "mod";

For the rare case of needing to import for side effects, this may be desirable - but for most cases you will not want to leave behind an unnecessary side effect import.

Examples

Examples of incorrect code for this rule:

import { type A } from "mod";
import { type A as AA } from "mod";
import { type A, type B } from "mod";
import { type A as AA, type B as BB } from "mod";

Examples of correct code for this rule:

import type { A } from "mod";
import type { A as AA } from "mod";
import type { A, B } from "mod";
import type { A as AA, B as BB } from "mod";

How to use

To enable this rule in the CLI or using the config file, you can use:

CLI

oxlint --deny typescript/no-import-type-side-effects

Config (.oxlintrc.json)

{
  "rules": {
    "typescript/no-import-type-side-effects": "error"
  }
}

References

• Rule Source