174 - Migrating from JavaScript to TypeScript (Javascript)

TypeScript – Migrating from JavaScript to TypeScript

Migrating your JavaScript project to TypeScript can be a beneficial step, as TypeScript offers static type checking and improved tooling for better code quality and maintainability. In this guide, we’ll explore how to migrate from JavaScript to TypeScript, step by step.

1. Setting Up TypeScript

The first step in the migration process is to set up TypeScript in your project. You can use npm or yarn to install TypeScript and its compiler, TSC:


npm install typescript --save-dev

After installation, you’ll need to create a `tsconfig.json` file in your project’s root directory. This file configures TypeScript for your project. A basic `tsconfig.json` might look like this:


{
  "compilerOptions": {
    "target": "ES6",
    "module": "CommonJS",
    "outDir": "./dist",
    "rootDir": "./src"
  },
  "include": ["src/**/*.ts"],
  "exclude": ["node_modules"]
}

Be sure to adjust the configuration according to your project’s needs.

2. Renaming JavaScript Files to TypeScript

Now it’s time to rename your existing JavaScript files with a `.js` extension to TypeScript files with a `.ts` extension. This change tells TypeScript to treat these files as TypeScript code. You can rename a JavaScript file like this:


mv myScript.js myScript.ts

Repeat this step for all the JavaScript files you want to migrate.

3. Type Annotation and Declarations

TypeScript shines when you add type annotations to your variables and functions. Start by annotating the types of your variables, function parameters, and return values. Here’s an example:


// JavaScript
function add(a, b) {
  return a + b;
}

// TypeScript
function add(a: number, b: number): number {
  return a + b;
}

By adding these type annotations, you make your code more explicit and TypeScript can catch type-related errors during development.

4. Handling Modules

If your project uses JavaScript modules, you’ll want to take advantage of TypeScript’s module system. Use `import` and `export` statements to define your module dependencies. Here’s a sample:


// JavaScript module
// math.js
export function add(a, b) {
  return a + b;
}

// TypeScript module
// math.ts
export function add(a: number, b: number): number {
  return a + b;
}

Switching to TypeScript modules helps manage your project’s dependencies and improves maintainability.

5. Enabling TypeScript Features

As you work with TypeScript, you can leverage advanced features like interfaces, classes, and generics. Here’s a brief overview:

Interfaces: Define contracts for objects, helping you maintain code consistency.
Classes: Create reusable and structured components with constructors and methods.
Generics: Write functions and data structures that work with different data types while preserving type safety.

Gradually introduce these features to enhance your codebase.

6. Running TypeScript Compiler

Before using your TypeScript code, you need to compile it into JavaScript. Use the TypeScript compiler (TSC) to perform this task. You can run the compiler with the following command:


npx tsc

TSC compiles your TypeScript code based on the configuration specified in your tsconfig.json file.

7. Debugging and Testing

It’s important to thoroughly test and debug your TypeScript code to ensure it functions as expected. Use tools like VS Code with TypeScript support to assist in debugging. Run unit tests to validate the correctness of your code.

8. Incremental Migration

If your project is extensive, consider an incremental migration strategy. You can start by converting and testing one module at a time. Over time, migrate the entire project.

Conclusion

Migrating from JavaScript to TypeScript is a progressive process that can significantly improve your code’s quality and maintainability. By following the steps outlined in this guide, you can successfully transition to TypeScript and enjoy the benefits of static typing and enhanced tooling.

174 – Migrating from JavaScript to TypeScript (Javascript)