eslint-plugin-no-explicit-type-exports

This plugin guards against attempting to export types that may not exist after type extraction. This usually occurs when you have a file that exports an imported type.

Example Usage

Imagine a you have a typescript package that includes foo.ts and index.ts:

// foo.ts
export type barType = string;

// index.ts
export { barType } from './foo.ts';

When foo.ts is built into JavaScript, the types are removed and added to a type declaration file. However, the export statement in index.ts will not be removed. When another developer tries to use this package in a JavaScript project they can encounter errors that the export doesn't actually exist.

 ./node_modules/some_repo/index.js
 attempted import error: 'barType' is not exported from './foo'.

Installation

yarn add --dev eslint-plugin-no-explicit-type-exports

Usage

In your .eslintrc add eslint-plugin-no-explicit-type-exports to the plugin section.

{
  "plugins": ["eslint-plugin-no-explicit-type-exports"],
  "rules": {
    "no-explicit-type-exports/no-explicit-type-exports": 2
  }
}

Note: you will need to use the @typescript-eslint/parser and add an import/resolver to your eslint settings. More information about import/resolver can be found in the eslints-plugin-import documentation. Links to both @typescript-eslint and eslints-plugin-import can be found at the bottom of this README.

{
  "parser": "@typescript-eslint/parser",
  "parserOptions": {
    "project": "./tsconfig.json",
    "sourceType": "module"
  },
  "plugins": ["@typescript-eslint"],
    "settings": {
    "import/resolver": {
      "node": {
        "extensions": [".js", ".jsx", ".ts", ".tsx"]
      }
    }

Rule Details

given:

// foo.ts
export type aType = string;

export randomNumber = 5;

export interface anInterface {
    bar: string;
}

// bar.ts
interface anInterface {
    a: string;
    b: number;
}

type aType = string;

const randomNumber = 5;

export {aType, anInterface};
export default randomNumber;

// baz.ts
type aType = string;

export default aType;

// oneLine.ts
export type x = keyof typeof String;

Valid:

import { aType, randomNumber, anInterface } from './foo';

import {aType, randomNumber, anInterface} from './foo';

export randomNumber;

// exporting * is valid. Since types and interfaces are already stript out
import { aType, randomNumber, anInterface } from './foo';

export * from './foo';

Invalid:

import {aType, randomNumber, anInterface} from './foo';

export anInterface;

import {aType, randomNumber, anInterface} from './foo';

export aType;

export { aType } from './baz';

export { x } from './oneLine';

Fixable

The --fix option will add the 'type' operator to all types and interfaces that are imported then exported from a file.

This:

import { SomeThing } from './some-module.js';
export { SomeThing };

Will be fixed to:

import type { SomeThing } from './some-module.js';
export type { SomeThing };

Further Reading

This plugin uses the eslints-plugin-import resolver to resolve the files that I would be accessing to check if the specifier was a type or an interface. https://github.com/benmosher/eslint-plugin-import

It also uses the @typescript-eslint/parse to parse files to check for types.

https://github.com/typescript-eslint/typescript-eslint

Contributing

Contributions are welcome! If you encounter problems or have a feature suggestion we'd love to hear about it. Open an issue in the GitHub issue tracker and we will do our best to provide support. Thank you!