When working with TypeScript, maintaining code quality and consistency is important. ESLint, a powerful linting tool for JavaScript and TypeScript, helps developers stick to coding standards and catch errors early. This article will guide you through setting up ESLint with TypeScript to ensure your code remains clean, readable, and error-free.

Prerequisites

• Node.js: Installed on your system.
• NPM (Node Package Manager)
• TypeScript

What is TypeScript ESLint?

TypeScript ESLint is a set of tools that allows ESLint, a popular JavaScript linting utility, to work with TypeScript code. It provides linting rules and configurations specifically designed to work with TypeScript, enhancing code quality and ensuring consistency across TypeScript projects.

Why Do We Use TypeScript ESLint?

TypeScript ESLint is used to maintain high code quality and consistency in TypeScript projects. It helps developers catch errors early, enforce coding standards, and improve code maintainability. By integrating ESLint with TypeScript, developers can use type information for more advanced linting rules that go beyond simple syntax checks.

Steps to Implement TypeScript eslint

Step 1: Initialize the Project

Create a new directory for your project and navigate into it:

mkdir typescript-eslint-project
cd typescript-eslint-project

Step 2: Initialize a new Node.js project:

npm init -y

Step 3: Install Dependencies

Install TypeScript and ESLint along with necessary plugins:

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

Folder Structure

Dependencies

"devDependencies": {
    "@typescript-eslint/eslint-plugin": "^7.16.1",
    "@typescript-eslint/parser": "^7.16.1",
    "eslint": "^8.57.0",
    "typescript": "^5.5.3"
}

Step 4: Configure TypeScript

Create a tsconfig.json file in the project root with the following content:

//tsconfig.json

{
    "compilerOptions": {
        "target": "ES6",
        "module": "commonjs",
        "strict": true,
        "esModuleInterop": true,
        "skipLibCheck": true,
        "forceConsistentCasingInFileNames": true
    },
        "include": [ "src" ]
}

Step 5: Configure ESLint

Create an .eslintrc.json file in the project root with the following content:

//.eslintrc.json file

{
    "parser": "@typescript-eslint/parser",
        "extends":
            [
                "eslint:recommended",
                "plugin:@typescript-eslint/recommended"
            ],
        "parserOptions":
            {"ecmaVersion": 2020, "sourceType": "module"},
        "rules": {
            // Add your custom rules here
        }
}

Step 6: Write Sample TypeScript Code

Create a src/index.ts file with the following content:

// src/index.ts
const greet = (name: string): string => {
    return `Hello, ${name}!`;
};

const unusedVar = 42; // This should trigger a warning or error

console.log(greet('World'));

Step 7: Run and Verify

Run ESLint to check for issues in your TypeScript code:

npx eslint src/**/*.ts

Output

Related Terms

• Shared Configs: Shared configs are reusable ESLint configurations that can be extended in multiple projects. They help maintain consistency across different projects by centralizing common linting rules.
• Dependency Versions: Dependency versions refer to the specific versions of ESLint, TypeScript, and other related packages required for TypeScript ESLint to function correctly. Keeping these dependencies up-to-date ensures compatibility and access to the latest features and fixes.
• Releases: Releases are the updates or new versions of TypeScript ESLint that include new features, bug fixes, and improvements. Keeping track of releases is important to benefit from the latest enhancements.
• Versioning: TypeScript ESLint follows semantic versioning, where version numbers reflect the nature of changes (major, minor, or patch). This helps developers understand the impact of updating to a new version.
• Formatting: Formatting tools like Prettier can be integrated with ESLint to ensure consistent code formatting. Using eslint-config-prettier and eslint-plugin-prettier, you can disable ESLint rules that conflict with Prettier and run Prettier as an ESLint rule.
• TSLint: TSLint was the original linter for TypeScript but is now deprecated in favor of TypeScript ESLint. Projects are encouraged to migrate from TSLint to TypeScript ESLint for better support and features.

Related Packages

1. eslint-plugin

eslint-plugin provides a set of ESLint rules specifically for TypeScript, helping enforce coding standards and best practices.

Syntax:

npm install --save-dev eslint-plugin

2. eslint-plugin-tslint

eslint-plugin-tslint allows using TSLint rules within ESLint, facilitating a smoother migration from TSLint to TypeScript ESLint.

Syntax:

npm install --save-dev eslint-plugin-tslint

3. parser

@typescript-eslint/parser is the parser that allows ESLint to understand TypeScript syntax and leverage TypeScript's type information.

4. rule-tester

@typescript-eslint/rule-tester is a utility to help test custom ESLint rules.

Syntax:

npm install --save-dev @typescript-eslint/rule-tester

5. scope-manager

@typescript-eslint/scope-manager manages the scope of variables and functions, crucial for implementing ESLint rules that understand TypeScript's type system.

Syntax:

npm install --save-dev @typescript-eslint/scope-manager

6. type-utils

@typescript-eslint/type-utils provides utilities for working with TypeScript types within ESLint rules.

Syntax:

npm install --save-dev @typescript-eslint/type-utils

7. typescript-estree

@typescript-eslint/typescript-estree is responsible for converting TypeScript code into an Abstract Syntax Tree (AST) that ESLint can understand and process.

Syntax:

npm install --save-dev @typescript-eslint/typescript-estree

8. typescript-eslint

@typescript-eslint is the main package that bundles all the necessary tools and plugins to integrate TypeScript with ESLint.

Syntax:

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

9. utils

@typescript-eslint/utils includes various utility functions to simplify the creation and management of ESLint rules for TypeScript.