How to Write TypeScript Plugins for Babel and ESLint

TypeScript plugins for Babel and ESLint allow developers to extend and customize the behavior of these tools to fit specific project needs. Babel is a popular JavaScript compiler, and ESLint is a widely used linter for ensuring code quality. Writing custom plugins can streamline development workflows and enforce coding standards in TypeScript projects.

Step 1: Writing a Custom TypeScript Plugin for Babel

To create a Babel plugin for TypeScript, follow these steps:

1.1 Install Required Dependencies

Start by installing Babel and the necessary dependencies for building a plugin:

npm install --save-dev @babel/core @babel/preset-typescript @babel/plugin-syntax-typescript

1.2 Create the Plugin Structure

Next, create the structure for your Babel plugin:

• src/index.ts - The entry point for the plugin

1.3 Implement the Babel Plugin

Write the plugin by exporting a function that Babel will use to transform code. Here's an example plugin that transforms TypeScript types:

import { types as t, NodePath } from '@babel/core';

export default function myTypeScriptPlugin() {
  return {
    visitor: {
      TSTypeAliasDeclaration(path: NodePath<t.TSTypeAliasDeclaration>) {
        // Example: log each TypeScript type alias declaration
        console.log(path.node.id.name);
      },
    },
  };
}

This plugin logs each TypeScript type alias found during compilation.

1.4 Use the Plugin in Babel

To use the plugin, configure Babel by adding it to your .babelrc or babel.config.js:

{
  "presets": ["@babel/preset-typescript"],
  "plugins": ["./path-to-your-plugin"]
}

Step 2: Writing a Custom TypeScript Plugin for ESLint

Now, let's create a custom TypeScript plugin for ESLint. This can be useful for enforcing project-specific linting rules.

2.1 Install Required Dependencies

First, install ESLint and its TypeScript-related plugins:

npm install --save-dev eslint @typescript-eslint/parser @typescript-eslint/eslint-plugin

2.2 Create a Custom ESLint Rule

In this example, we'll create a custom ESLint rule that enforces a naming convention for TypeScript interfaces:

import { TSESTree } from "@typescript-eslint/types";
import { Rule } from "eslint";

const rule: Rule.RuleModule = {
  meta: {
    type: "suggestion",
    docs: {
      description: "Enforce interface names to start with I",
      category: "Stylistic Issues",
    },
    schema: [], // no options
  },
  create(context) {
    return {
      TSInterfaceDeclaration(node: TSESTree.TSInterfaceDeclaration) {
        if (!/^I[A-Z]/.test(node.id.name)) {
          context.report({
            node,
            message: "Interface name '{{ name }}' should start with 'I'.",
            data: { name: node.id.name },
          });
        }
      },
    };
  },
};

export default rule;

2.3 Integrate the Custom Rule

Once the rule is written, you can integrate it into your ESLint configuration:

{
  "parser": "@typescript-eslint/parser",
  "plugins": ["@typescript-eslint"],
  "rules": {
    "my-custom-rule": "error"
  }
}

Step 3: Testing and Debugging Plugins

After writing your Babel and ESLint plugins, it's essential to test them. Create a TypeScript file with the relevant patterns and run Babel or ESLint to see if the plugins work as expected.

To test the Babel plugin, run:

npx babel src --out-dir lib --extensions .ts

To test the ESLint plugin, run:

npx eslint src --ext .ts

Conclusion

Creating custom TypeScript plugins for Babel and ESLint allows for fine-grained control over your codebase's compilation and linting process. By following these steps, you can extend both tools to suit your project's specific needs and improve the overall developer experience.