JS.TS.CONSISTENT.TYPE.EXPORTS

TypeScript 3.8 added support for type-only exports.

Type-only exports allow you to specify that 1 or more named exports are exported as type-only. This allows transpilers to drop exports without knowing the types of the dependencies.

Rule Details

This rule aims to standardize the use of type exports style across a codebase.

Given a class Button, and an interface ButtonProps, examples of code:

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Incorrect

interface ButtonProps {
  onClick: () => void;
}
class Button implements ButtonProps {
  onClick() {
    console.log('button!');
  }
}
export { Button, ButtonProps };

Correct

interface ButtonProps {
  onClick: () => void;
}
class Button implements ButtonProps {
  onClick() {
    console.log('button!');
  }
}
export { Button };
export type { ButtonProps };

Options

interface Options {
  fixMixedExportsWithInlineTypeSpecifier?: boolean;
}

const defaultOptions: Options = {
  fixMixedExportsWithInlineTypeSpecifier: false,
};

fixMixedExportsWithInlineTypeSpecifier

When this is set to true, the rule will autofix "mixed" export cases using TS 4.5's "inline type specifier". If you are using a TypeScript version less than 4.5, then you will not be able to use this option.

For example the following code:

const x = 1;
type T = number;

export { x, T };

With {fixMixedExportsWithInlineTypeSpecifier: true} will be fixed to:

const x = 1;
type T = number;

export { x, type T };

With {fixMixedExportsWithInlineTypeSpecifier: false} will be fixed to:

const x = 1;
type T = number;

export type { T };
export { x };

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Incorrect

export { Button } from 'some-library';
export type { ButtonProps } from 'some-library';

Correct

export { Button, type ButtonProps } from 'some-library';

When Not To Use It

• If you are using a TypeScript version less than 3.8, then you will not be able to use this rule as type exports are not supported.
• If you specifically want to use both export kinds for stylistic reasons, you can disable this rule.
• If you use --isolatedModules the compiler would error if a type is not re-exported using export type. If you also don't wish to enforce one style over the other, you can disable this rule.