Typescript Linting With Tslint Eslint Complete Guide

 Last Update:2025-06-22T00:00:00     .NET School AI Teacher - SELECT ANY TEXT TO EXPLANATION.    7 mins read      Difficulty-Level: beginner

Understanding the Core Concepts of TypeScript Linting with TSLint ESLint

Explaining TypeScript Linting with TSLint and ESLint in Detail

Understanding TypeScript

Before delving into linting, let’s briefly revisit TypeScript, a statically typed language built on JavaScript. TypeScript adds static typing, classes, and interfaces, which improve the quality of code by catching errors early and providing more robust code structures.

Introduction to Linting

Linting tools analyze your source code and ensure it adheres to a set of stylistic or quality rules. These rules can range from indentation and variable naming conventions to more complex structural issues and best practices. Linting helps maintain a consistent code style and prevents common pitfalls.

TSLint: The Traditional TypeScript Linter

TSLint was the original TypeScript-specific linter. It was developed by Microsoft and was widely used in large TypeScript projects. TSLint’s primary purpose was to enforce coding style and identify errors, leveraging TypeScript’s type system to offer more specific checks.

Important Features and Benefits of TSLint:
  1. Type Awareness: TSLint leverages TypeScript’s type information to provide more precise and meaningful checks.
  2. Rule-based: Offers a customizable set of rules that can be extended.
  3. Integration: Works seamlessly with TypeScript and integrates with build systems like Gulp and Webpack.
Drawbacks of TSLint:

Despite its strengths, TSLint faced several issues:

  • It was designed primarily for static analysis and didn’t support AST traversal rules.
  • TSLint has been deprecated in favor of ESLint due to its more comprehensive feature set and better extensibility.

ESLint: The Modern JavaScript and TypeScript Linter

ESLint is a widely adopted linting tool for JavaScript. It has since evolved to support TypeScript through plugins and integrations, making it a versatile choice.

Important Features and Benefits of ESLint:
  1. Extensibility: Offers a rich ecosystem of plugins and rules that can be customized and extended to fit specific needs.
  2. AST-based: Uses Abstract Syntax Trees (AST) for better analysis and support of complex coding patterns.
  3. Integration: Integrates well with build tools, editors, and continuous integration systems.
  4. Performance: Optimized for performance, making it suitable for large codebases.
  5. Community and Support: Backed by a large community, ensuring ongoing development and improvements.
Using ESLint for TypeScript:

To use ESLint with TypeScript, you need to set up a few configurations:

  1. Installation: Install ESLint and the TypeScript ESLint plugin: 
    npm install eslint @typescript-eslint/parser @typescript-eslint/eslint-plugin --save-dev
  2. Configuration File (.eslintrc.js): Set up your configuration file to include necessary rules: 
    module.exports = {
  parser: '@typescript-eslint/parser',
  extends: [
    'eslint:recommended',
    'plugin:@typescript-eslint/recommended'
  ],
  plugins: ['@typescript-eslint'],
  rules: {
    // Override or add custom rules
  }
};
  3. Integrating with Editor: Install and configure ESLint plugins for your IDE (e.g., VSCode, WebStorm) to get real-time feedback.

Choosing Between TSLint and ESLint

Considering TSLint’s deprecation, the transition to ESLint for TypeScript projects is recommended. ESLint offers superior extensibility, performance, and community support.

Conclusion

Linting is an essential part of the software development process, and when it comes to TypeScript projects, tools like TSLint and ESLint are invaluable. While TSLint provides specific benefits for TypeScript, ESLint’s broader ecosystem and ongoing development make it the preferred choice moving forward. Ensuring your TypeScript project is well-linted not only improves code quality but also leads to more maintainable and efficient codebases.

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Step-by-Step Guide: How to Implement TypeScript Linting with TSLint ESLint

Part 1: Setting up TSLint

TSLint has been deprecated in favor of ESLint, but for completeness, here’s how you might set up TSLint.

Step 1: Initialize a Project

First, initialize a new npm project. If you haven't already created a new project directory, do so:

mkdir ts-linting-example
cd ts-linting-example

Then run:

npm init -y

Step 2: Install TypeScript

Install TypeScript if you haven't already:

npm install typescript --save-dev

You can also create a TypeScript configuration file by running:

npx tsc --init

Step 3: Install TSLint

Now, install TSLint and some rules that TSLint can use:

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

Step 4: Create TSLint Configuration

Create a tslint.json file in your project root. Add some basic rules:

{
  "defaultSeverity": "warning",
  "extends": ["tslint:recommended"],
  "jsRules": {},
  "rules": {
    "quotemark": [true, "single"],
    "semicolon": [true, "never"]
  },
  "rulesDirectory": []
}

Step 5: Create a TypeScript File

Create a src directory and add a TypeScript file, app.ts:

mkdir src
touch src/app.ts

Add some TypeScript code to app.ts:

console.log('Hello, world!');
const x: number = 5;
console.log(x);

Step 6: Add a Script to Run TSLint

Edit your package.json to add a script for linting:

"scripts": {
  "lint": "tslint -p tsconfig.json"
}

Step 7: Run TSLint

Run the following command to lint your files:

npm run lint

Part 2: Setting up ESLint

TSLint is deprecated. Instead, you should use ESLint with TypeScript.

Step 1: Initialize a New Project (if starting fresh)

If you're starting fresh, initialize a new npm project:

mkdir ts-linting-example eslint
cd ts-linting-example-eslint

Then:

npm init -y

Step 2: Install TypeScript

Install TypeScript:

npm install typescript --save-dev

Create a TypeScript configuration file:

npx tsc --init

Step 3: Install ESLint

Install ESLint and the necessary plugins and parser:

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

Step 4: Create ESLint Configuration

Create an .eslintrc.json file in your project root and add some basic rules:

{
  "parser": "@typescript-eslint/parser",
  "plugins": ["@typescript-eslint"],
  "extends": [
    "eslint:recommended",
    "plugin:@typescript-eslint/recommended"
  ],
  "rules": {
    "quotes": ["error", "single"],
    "semi": ["error", "never"],
    "@typescript-eslint/no-unused-vars": ["warn"]
  }
}

Step 5: Create a TypeScript File

If you haven’t already, create a src directory and add a TypeScript file, app.ts:

mkdir src
touch src/app.ts

Add the same TypeScript code to app.ts:

console.log('Hello, world!');
const x: number = 5;
console.log(x);

Step 6: Add a Script to Run ESLint

Edit your package.json to add a script for linting:

"scripts": {
  "lint": "eslint 'src/**/*.ts'"
}

Step 7: Run ESLint

Run the following command to lint your files:

Top 10 Interview Questions & Answers on TypeScript Linting with TSLint ESLint

1. What is TypeScript Linting, and Why is it Important?

Answer:
TypeScript linting involves using static analysis tools to enforce coding standards and best practices in your TypeScript code. It helps in identifying and fixing potential issues early on, improving code quality, consistency, and maintainability. Linters also ensure adherence to team or project-specific coding guidelines, reducing the likelihood of bugs and making the codebase more predictable.

2. What are TSLint and ESLint? How do They Differ?

Answer:

  • TSLint: Originally the main TypeScript linter, designed specifically for TypeScript. It was widely used but is no longer actively maintained since its creators recommended moving to ESLint.
  • ESLint: Primarily a JavaScript linter that later gained support for TypeScript via plugins. It is more flexible, actively maintained, and integrates seamlessly with a broader ecosystem of tools and plugins.

Key Differences:

  • Language Support: ESLint covers both JavaScript and TypeScript, while TSLint was TypeScript-only.
  • Community and Maintenance: ESLint has a larger community and is actively maintained, offering more frequent updates and features.
  • Extensibility: ESLint is highly extensible, allowing for more customized linting rules and integration with various tools and frameworks.

3. How do I Install ESLint for TypeScript Projects?

Answer:
To set up ESLint with TypeScript, follow these steps:

  1. Install ESLint and Required Packages:

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

  2. Initialize ESLint Configuration:

    npx eslint --init

    Follow the prompts to set up your configuration. Choose TypeScript as the language and any other options that fit your project needs.

  3. Configure ESLint: In your .eslintrc or .eslintrc.js file, add the parser and plugins for TypeScript:

    {
  "parser": "@typescript-eslint/parser",
  "plugins": ["@typescript-eslint"],
  "extends": [
    "eslint:recommended",
    "plugin:@typescript-eslint/recommended"
  ]
}

  4. Add a Script for Linting: In your package.json:

    "scripts": {
  "lint": "eslint 'src/**/*.ts'"
}

  5. Run ESLint:

    npm run lint

4. What are Some Essential Linting Rules for TypeScript Projects?

Answer:
Here are some essential rules for TypeScript linting:

  • @typescript-eslint/explicit-module-boundary-types: Ensures that function return types are explicitly defined.
  • @typescript-eslint/no-explicit-any: Disallows the use of any type, encouraging more specific types.
  • @typescript-eslint/no-unused-vars: Detects and reports unused variables.
  • @typescript-eslint/naming-convention: Enforces naming conventions for variables, functions, classes, etc.
  • @typescript-eslint/no-empty-interface: Flags empty interfaces that could be removed.
  • @typescript-eslint/ban-ts-comment: Disallows certain ts- comments (e.g., ts-ignore) that can hide issues.
  • @typescript-eslint/no-shadow: Prevents variable shadowing to maintain code clarity.
  • @typescript-eslint/quotes: Enforces consistent use of single or double quotes.
  • @typescript-eslint/consistent-type-assertions: Ensures type assertions use the as syntax.
  • @typescript-eslint/no-namespace: Discourages the use of namespaces in favor of modules.

5. How do I Integrate ESLint with a TypeScript Project Using VSCode?

Answer:
To integrate ESLint with your TypeScript projects in VSCode, follow these steps:

  1. Install ESLint Extension:

    • In VSCode, go to the Extensions view (Ctrl+Shift+X).
    • Search for "ESLint" and install the extension by Dirk Baeumer.

  2. Configure ESLint:

    • Ensure ESLint is installed and configured in your project (as described in Q3).
    • Optionally, add settings to your .vscode/settings.json for better integration: 
      {
  "eslint.enable": true,
  "eslint.autoFixOnSave": true,
  "editor.codeActionsOnSave": {
    "source.fixAll.eslint": true
  },
  "eslint.validate": [
    "javascript",
    "javascriptreact",
    "typescript",
    "typescriptreact"
  ]
}

  3. Open Terminal and Run Linter:

    • Use the integrated terminal to run npm run lint or npx eslint for on-demand linting.

  4. View and Fix Issues:

    • Errors and warnings will appear in the Problems panel and directly in your editor.
    • Use the suggested fixes from the editor to automatically resolve issues when possible.

6. What are the Benefits of Migrating from TSLint to ESLint for TypeScript Projects?

Answer:
Migrating from TSLint to ESLint offers several benefits:

  • Unified Tooling: ESLint supports both JavaScript and TypeScript, eliminating the need for separate tools.
  • Active Development: ESLint has a larger community and is actively maintained, ensuring new rules and features.
  • Rich Plugin Ecosystem: ESLint's extensive plugin system allows for highly customizable linting configurations.
  • Performance Improvements: ESLint can be optimized for performance, especially in large codebases.
  • Better Integration: Seamlessly integrates with other modern toolchains and build systems.
  • Consistency: Using a single linter across different projects (JavaScript + TypeScript) ensures consistent coding standards and practices.

7. How do I Migrate an Existing Project from TSLint to ESLint?

Answer:
Migrating from TSLint to ESLint involves a few steps to ensure a smooth transition:

  1. Install ESLint and Necessary Packages:

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

  2. Initialize ESLint Configuration:

    npx eslint --init

    Follow the prompts to configure ESLint for TypeScript.

  3. Update ESLint Configuration: In your .eslintrc or .eslintrc.js file, include necessary configurations:

    {
  "parser": "@typescript-eslint/parser",
  "plugins": ["@typescript-eslint"],
  "extends": [
    "eslint:recommended",
    "plugin:@typescript-eslint/recommended"
  ]
}

  4. Migrate TSLint Rules:

    • Use tools like tslint-to-eslint-config to automatically convert your existing TSLint configuration to ESLint.
    • Example usage: 
      npx tslint-to-eslint-config
    • Manually adjust any remaining rules or configurations that weren’t automatically translated.

  5. Test ESLint: Run ESLint on your code to ensure all rules are working correctly:

    npm run lint

  6. Update CI/CD Pipelines: Ensure your CI/CD pipelines are updated to use ESLint instead of TSLint.

  7. Remove TSLint Configuration: After confirming everything is working, you can remove TSLint and its configuration files from your project.

8. How do I Customize ESLint Rules for My Team's Coding Standards?

Answer:
Customizing ESLint rules to align with your team's coding standards involves several steps:

  1. Create or Update ESLint Configuration File:

    • This is typically .eslintrc.json, eslintrc.js, or .eslintrc.yml.
    • Example configuration file: 
      {
  "parser": "@typescript-eslint/parser",
  "plugins": ["@typescript-eslint"],
  "extends": [
    "eslint:recommended",
    "plugin:@typescript-eslint/recommended"
  ],
  "rules": {
    // Custom rules
    "@typescript-eslint/explicit-module-boundary-types": "error",
    "@typescript-eslint/no-explicit-any": "warn",
    "quotes": ["error", "single"],
    "semi": ["error", "always"],
    // Add other custom rules here
  }
}

  2. Add/Modify Rules:

    • Specific Rules: Define or modify individual rules to suit your needs (e.g., enforcing line breaks, spacing, naming conventions).
    • Rule Sets: Use rule sets from other configurations (e.g., Airbnb, Google) and customize them.

  3. Use Shared Configurations:

    • Create a shared ESLint configuration package if multiple projects follow the same rules.
    • Publish the configuration package and import it in your projects: 
      "extends": ["@yourorg/eslint-config"]

  4. Override Rules for Specific Files:

    • Use overrides in your configuration to apply different rules to specific files or directories.
    • Example: 
      {
  "overrides": [
    {
      "files": ["*.test.ts", "*.spec.ts"],
      "rules": {
        "@typescript-eslint/no-unused-vars": "off"
      }
    }
  ]
}

  5. Document and Educate Your Team:

    • Provide documentation for the custom rules and their reasoning.
    • Train your team on the new linting standards and how to fix reported issues.

  6. Automate and Enforce:

    • Integrate ESLint checks into your CI/CD pipeline to enforce adherence to the coding standards.
    • Use the --fix option during linting to automatically apply fixes where possible.

9. How do I Handle ESLint Performance Issues in Large Codebases?

Answer:
Handling ESLint performance issues in large codebases is crucial to maintain a smooth development workflow. Here are some strategies:

  1. Optimize ESLint Configuration:

    • Rule Selection: Limit the number of rules to only those necessary.
    • Specificity: Use overrides to apply rules only to specific files or directories, reducing unnecessary checks.
    • Rule Complexity: Avoid complex and computationally expensive rules.

  2. Use .eslintignore:

    • Include files and directories that do not need linting, such as built files, generated code, or third-party libraries.
    • Example: 
      node_modules/
dist/
.vscode/
*.config.js

  3. Incremental Linting:

    • Use ESLint’s --fix-dry-run or --fix options to apply fixes automatically.
    • Configure your editor or IDE to run linting only on modified files during development.

  4. Parallel Linting:

    • Use tools like eslint-plugin-concurrent-files to run ESLint on multiple files in parallel.
    • Integrate with task runners like lint-staged or husky to run linting checks on staged files only.

  5. Profile ESLint Performance:

    • Use ESLint’s --print-config option to inspect the final configuration and identify potentially expensive rules.
    • Analyze ESLint’s performance using profiling tools or by running ESLint with the --debug flag.

  6. Leverage Caching:

    • Use ESLint’s caching features to skip linting files that haven’t changed since the last run.
    • Configure caching in your ESLint configuration: 
      {
  "cache": true,
  "cacheLocation": ".eslintcache"
}

  7. Optimize Parser Options:

    • Ensure that your parser configuration is optimized to handle your codebase efficiently.
    • For example, using project option with @typescript-eslint/parser for more precise type checking: 
      {
  "parserOptions": {
    "project": "./tsconfig.json",
    "tsconfigRootDir": __dirname
  }
}

  8. Upgrade ESLint:

    • Keep ESLint and its plugins up to date to benefit from performance improvements and bug fixes.
    • Regularly check for new releases and update dependencies accordingly.

  9. Split Linting Tasks:

    • Split linting tasks across different CI/CD jobs to parallelize the process.
    • Use separate jobs for different parts of your codebase, such as different directories or modules.

  10. Monitor and Iterate:

    • Continuously monitor ESLint performance and iterate on your configurations based on actual usage.
    • Collect feedback from your team and make adjustments to improve performance and maintainability.

10. How do I Integrate ESLint with Popular Frameworks like React, Angular, Vue, etc.?

Answer:
Integrating ESLint with popular frameworks involves setting up project-specific configurations and using appropriate plugins. Below are guides for React, Angular, and Vue.

React with TypeScript:

  1. Install ESLint and Additional Packages:

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

  2. Initialize ESLint Configuration:

    npx eslint --init

    Choose the appropriate options for a React project with TypeScript.

  3. Configure ESLint:

    {
  "parser": "@typescript-eslint/parser",
  "parserOptions": {
    "project": "./tsconfig.json",
    "tsconfigRootDir": __dirname,
    "ecmaFeatures": {
      "jsx": true
    }
  },
  "plugins": ["@typescript-eslint", "react", "react-hooks"],
  "extends": [
    "eslint:recommended",
    "plugin:@typescript-eslint/recommended",
    "plugin:react/recommended",
    "plugin:react-hooks/recommended",
    "plugin:jsx-a11y/recommended"
  ],
  "settings": {
    "react": {
      "version": "detect"
    }
  }
}

  4. Run ESLint:

    npm run lint

Angular with TypeScript:

  1. Install ESLint and Additional Packages:

    ng add @angular-eslint/schematics

  2. Set Up ESLint: Angular CLI handles the setup automatically, integrating ESLint with your Angular project.

  3. Customize Configuration: Modify the generated .eslintrc.json or tslint.json (if using legacy TSLint setup) to add custom rules.

  4. Run ESLint:

    ng lint

  5. Migrate from TSLint to ESLint: If using legacy TSLint, migrate to ESLint as described in Q7.

Vue with TypeScript:

  1. Install ESLint and Additional Packages:

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

  2. Initialize ESLint Configuration:

    npx eslint --init

    Choose the appropriate options for a Vue project with TypeScript.

  3. Configure ESLint:

    {
  "parser": "vue-eslint-parser",
  "parserOptions": {
    "parser": "@typescript-eslint/parser",
    "project": "./tsconfig.json",
    "tsconfigRootDir": __dirname,
    "ecmaVersion": 2020,
    "sourceType": "module"
  },
  "plugins": ["@typescript-eslint", "vue"],
  "extends": [
    "eslint:recommended",
    "plugin:@typescript-eslint/recommended",
    "plugin:vue/recommended"
  ],
  "rules": {
    // Add custom rules here
  }
}

  4. Run ESLint:

    npm run lint

By following these steps, you can effectively integrate ESLint with popular frameworks, ensuring consistent code quality and adherence to best practices.

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