TypeScript = JS+ types + compile-time safety

• Catches errors before runtime (compile-time errors)
• Improves code readability and maintainability
• Supports modern JS features and integrates with frameworks (React, Angular, Node.js)

TS cannot run in browser or Node.js:

1. TypeScript files (.ts or .tsx) are transpiled to JavaScript.

2. Type Checking

   • TypeScript compiler (tsc) analyzes code using the types you defined.
   • Errors like wrong types, missing properties, etc., are caught before JS is generated.

   let age:number = "25";
   // ❌ Error: Type 'string' is not assignable to type 'number'
   

3. Transpiling

   • TS removes type annotations and generates plain JS.

   // TypeScript (example.ts)
   let age: number = 25;
   console.log(age);
   
   // Compiled JavaScript (example.js)
   // : number is removed because JS doesn’t support types
   var age = 25;
   console.log(age);
   

4. Browsers or Node.js can execute.

5. Targeting JavaScript versions

   • TS can output different JS versions (ES5, ES6/ES2015, ESNext) depending on the target setting in tsconfig.json.

   {
     "compilerOptions": {
       "target": "ES5"
     }
   }
   

tsconfig.json

Configuration file for the TS compiler:

1. Which files to include/exclude
2. How to compile (JS version, modules, strictness, etc.)