How to Convert a JavaScript Project to TypeScript

Converting a JavaScript project to TypeScript can improve code quality and maintainability by adding static type checking. This guide provides a step-by-step process for converting an existing JavaScript project to TypeScript.

Step 1: Install TypeScript

Begin by adding TypeScript to the project. This is done using npm or yarn.

npm install typescript --save-dev

Step 2: Create a TypeScript Configuration File

Create a tsconfig.json file to configure TypeScript. This file specifies the compiler options and the files to include in the compilation.

{
  "compilerOptions": {
    "target": "es6",
    "module": "commonjs",
    "strict": true,
    "esModuleInterop": true,
    "skipLibCheck": true,
    "forceConsistentCasingInFileNames": true
  },
  "include": ["src/**/*"],
  "exclude": ["node_modules"]
}

Step 3: Rename JavaScript Files to TypeScript

Rename the JavaScript files from .js to .ts (or .jsx to .tsx if using React). This allows TypeScript to process these files.

• For files containing JSX, rename them to .tsx.
• For files with only TypeScript code, rename them to .ts.

Step 4: Add Type Definitions

Add type definitions for third-party libraries used in the project. These are available as @types packages on npm.

npm install @types/node @types/express --save-dev

Step 5: Fix TypeScript Errors

Compile the project using TypeScript and address any errors or type issues. TypeScript will provide feedback on type mismatches and other issues.

npx tsc

Step 6: Update Build Scripts

Update build scripts in package.json to use TypeScript. Modify scripts to include TypeScript compilation.

"scripts": {
  "build": "tsc",
  "start": "node dist/index.js"
}

Step 7: Test the Application

Run tests to ensure that the converted TypeScript code works as expected. Verify that the application behaves correctly after conversion.

Conclusion

Converting a JavaScript project to TypeScript involves installing TypeScript, configuring the compiler, renaming files, adding type definitions, and resolving errors. This process helps leverage TypeScript's features for better type safety and code maintainability.