TypeScript is a popular programming language that adds optional static typing and other features to JavaScript. ESLint is a tool for identifying and reporting on patterns found in JavaScript code, and is widely used in the JavaScript community for ensuring code quality and consistency. In this tutorial, we'll go through the steps required to set up ESLint with TypeScript in a Node.js project.


Install ESLint and TypeScript

The first step is to install ESLint and TypeScript in your Node.js project. You can do this using npm, the Node.js package manager. Open a terminal window and navigate to your project directory, then run the following command:

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

This installs the latest version of ESLint, along with the parser and plugin for TypeScript.


Configure ESLint for TypeScript

Next, we need to create an ESLint configuration file that specifies how ESLint should be used in our TypeScript project. Create a new file called .eslintrc.js in the root directory of your project, and add the following content:

module.exports = {
  parser: "@typescript-eslint/parser",
  plugins: ["@typescript-eslint"],
  extends: [
    "eslint:recommended",
    "plugin:@typescript-eslint/recommended"
  ],
  rules: {
    // your custom rules here
  }
};

This configuration file tells ESLint to use the TypeScript parser, and to enable the @typescript-eslint plugin. It also extends the recommended ESLint configuration and the recommended configuration for the @typescript-eslint plugin.


Add TypeScript-specific rules

ESLint comes with a number of built-in rules that are designed to work with vanilla JavaScript code. However, TypeScript introduces a number of additional features and syntax that require their own set of rules. The @typescript-eslint plugin provides a number of rules specifically for TypeScript, which we can add to our ESLint configuration file. Here are a few examples:

module.exports = {
  // ... other configuration options ...
  rules: {
    "@typescript-eslint/explicit-module-boundary-types": "off",
    "@typescript-eslint/no-unused-vars": ["error", { "argsIgnorePattern": "^_" }]
  }
};

The explicit-module-boundary-types rule ensures that functions that are exported from a module have their return type and parameter types explicitly defined. However, this can sometimes be cumbersome and redundant, so we've disabled this rule.

The no-unused-vars rule is similar to the built-in ESLint rule of the same name, but with added support for TypeScript's type annotations. In this example, we've configured the rule to ignore any function parameters whose name starts with an underscore.


Run ESLint

With ESLint and TypeScript configured, we can now run ESLint on our TypeScript code. To do this, run the following command in your terminal:

npx eslint src/**/*.ts

This tells ESLint to check all .ts files in the src directory and any subdirectories. If there are any issues with your code, ESLint will print them to the terminal.


Integrate with your IDE or text editor

Finally, it's useful to integrate ESLint with your IDE or text editor. This will allow you to see ESLint warnings and errors directly in your editor, as you write your code. There are a number of plugins available for different editors - check the ESLint documentation for details.


Conclusion

By following these steps, you can set up ESLint to work with TypeScript in your Node.js project. This will help you ensure that your code is consistent, error-free, and follows best practices in order to maintain good code quality and consistency throughout your project. Additionally, ESLint's ability to catch potential issues before they cause problems can save you a lot of time and effort in the long run.