Configuration (tsconfig.json)

When building a large TypeScript project, you won't use tsc index.ts repeatedly. Instead, you'll compile entire massive folders of .ts files synchronously.

To manage compiler rules, TypeScript uses a configuration file known as tsconfig.json.

Running the initialization command:

tsc --init

...generates a sprawling tsconfig.json file.

Crucial Compiler Options

Here are the most important properties you will interact with in a standard React or Node application:

{
  "compilerOptions": {
    /* Modules & Targets */
    "target": "ES2022",           // The version of JS the compiler outputs (e.g., ES5, ES2022) 
    "module": "CommonJS",         // Important for Node backward compatibility 
    "jsx": "react-jsx",           // Transforms TSX files into standard React calls

    /* Paths */
    "outDir": "./dist",           // Where the compiled pure .js files will be dumped
    "rootDir": "./src",           // Where TypeScript should search for source .ts files

    /* Strictness */
    "strict": true,               // ENABLES ALL STRICT TYPE-CHECKING RULES!
    "noImplicitAny": true,        // Prevents TypeScript from randomly guessing 'any' types
    "strictNullChecks": true,     // Makes Null and Undefined independently strict

    /* Interoperability */
    "esModuleInterop": true,      // Smooths out imports between ES modules and CommonJS
    "skipLibCheck": true          // Speeds up compile times by not type-checking node_modules
  },
  "include": ["src/**/*"],        // Tell TS which folders to compile
  "exclude": ["node_modules", "**/*.spec.ts"] // Folders specifically to ignore
}

Pro Tip: The "strict": true flag is the most important field. Without it, you are basically writing expensive Vanilla JS. Always keep strict mode enabled to ensure type safety!