Migrating JavaScript Projects to TypeScript

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In recent years, TypeScript has gained immense popularity among developers for its ability to bring static typing to JavaScript. This superset of JavaScript provides developers with the benefits of a robust type system, leading to fewer runtime errors and improved code maintainability. If you’re working on a JavaScript project and considering making the switch to TypeScript, this guide will walk you through the steps involved in migrating your codebase.

Why Migrate to TypeScript?

1. Strong Typing

JavaScript is dynamically typed, meaning you don’t declare variable types explicitly. While this flexibility is useful, it can lead to unexpected runtime errors. TypeScript introduces static typing, catching potential issues during development.

2. Improved Tooling Support

TypeScript offers enhanced tooling support with features like auto-completion, better code navigation, and refactoring capabilities. This can significantly boost developer productivity.

3. Better Code Documentation

With TypeScript, your code becomes more self-documenting. The type annotations serve as a form of documentation, making it easier for developers (including your future self) to understand and work with the code.

4. Easier Collaboration

TypeScript can be a great boon for teams. Clear type definitions reduce the chances of misunderstandings, making it easier for multiple developers to collaborate on the same codebase.

Getting Started

1. Setting Up TypeScript

Start by installing TypeScript in your project. If you’re using npm, run:

npm install typescript --save-dev

This will add TypeScript as a development dependency.

2. Creating a tsconfig.json

Next, you’ll need to create a tsconfig.json file in the root of your project. This file serves as the configuration for TypeScript. You can generate a basic tsconfig.json using the command:

npx tsc --init

This will create a default configuration file. You can customize it to fit your project’s needs.

3. Renaming Files to .ts or .tsx

TypeScript files have the extension .ts (or .tsx for files that include JSX). You’ll need to rename your existing .js files to .ts to start using TypeScript.

4. Enable Strict Mode

In the tsconfig.json file, set "strict": true. This will enable strict mode, which includes options like noImplicitAny, strictNullChecks, and more. Strict mode helps catch potential errors at compile time. Enabling strict mode is not mandatory, but it is recommended. To learn the advantages and potential drawbacks of enabling strict mode, visit this article.

The Migration Process

1. Start with a Small, Isolated Part of Your Project

Migrating an entire project at once can be overwhelming. Begin by selecting a small, less critical part of your codebase. This could be a single file or a module. Convert it to TypeScript and ensure it’s working as expected before moving on to larger sections.

2. Address Type Issues

As you convert JavaScript to TypeScript, you’ll likely encounter type-related issues. TypeScript may flag areas where types are unclear or incompatible. Address these issues by providing explicit type annotations.

3. Leverage DefinitelyTyped for External Libraries

If your project depends on external JavaScript libraries, you’ll need to find corresponding TypeScript type definitions. The DefinitelyTyped repository is a valuable resource for finding and installing type definitions for popular libraries.

4. Utilize JSDoc Annotations

When working with JavaScript code, you can use JSDoc comments to provide type information. TypeScript will recognize these annotations and use them for type checking. This can be especially useful when dealing with third-party libraries that don’t have TypeScript support.

Testing and Validation

1. Compile and Check

After making changes, run the TypeScript compiler to check for any errors:

npx tsc

Resolve any issues reported by the compiler before proceeding.

2. Thorough Testing

Test your code thoroughly to ensure that the changes haven’t introduced any new bugs. Pay close attention to areas where you’ve made significant modifications.

3. Code Reviews

If you’re working in a team, conduct code reviews to ensure that everyone is adhering to TypeScript best practices and catching any potential issues early on.


Migrating a JavaScript project to TypeScript can be a powerful step toward writing more reliable and maintainable code. While the process may initially seem daunting, starting with small, isolated sections and gradually expanding can make the transition smoother. Remember to leverage TypeScript’s strict mode and take advantage of tools like DefinitelyTyped for a seamless migration experience.

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Rajae Robinson

Rajae Robinson is a young Software Developer with over 3 years of work experience building websites and mobile apps. He has extensive experience with React.js and Next.js.

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