eslint-plugin-interface-to-type

An ESLint plugin that enforces the use of type aliases instead of interface declarations in TypeScript.

Installation

Install the plugin as a dev dependency:

npm install eslint-plugin-interface-to-type --save-dev

Usage

1. Add the plugin to your ESLint configuration file:

{
  "plugins": ["interface-to-type"]
}

2. Enable the rule in your ESLint configuration:

{
  "rules": {
    "interface-to-type/prefer-type-over-interface": "error"
  }
}

Rule: prefer-type-over-interface

This rule enforces the use of type aliases over interface declarations in TypeScript. See the full documentation in the docs/rules/prefer-type-over-interface.md.

Incorrect Code

interface User {
  id: number;
  name: string;
  role: 'admin' | 'user';
}

Correct Code

type User = {
  id: number;
  name: string;
  role: 'admin' | 'user';
};

Why interface can be risky

One of the reasons to prefer type over interface is the potential for unexpected behavior with interface merging. In TypeScript, when two interface declarations share the same name, they are automatically merged into a single declaration. This behavior, known as Declaration Merging, can introduce subtle bugs and unintended behaviors in your codebase.

Example of Declaration Merging

interface User {
  id: number;
}

interface User {
  name: string;
}

// Resulting type
interface User {
  id: number;
  name: string;
}

While this behavior can sometimes be useful, it often leads to confusion and makes code harder to maintain, especially in large or collaborative projects. Using type avoids this risk entirely, as type declarations with the same name will result in a compilation error.

Autofix

This rule supports ESLint's --fix option, which can automatically convert interface declarations to equivalent type aliases.

License

This project is licensed under the MIT License.