How TypeScript is different from JavaScript

TypeScript vs JavaScript – Key Differences with Examples:

Feature	JavaScript	TypeScript
Type System	Dynamically typed	Statically typed (with optional annotations)
Compilation	Interpreted in browser (no compile step)	Compiled to JavaScript before running
Error Detection	Errors are found at runtime	Errors are caught at compile-time
OOP Support	Limited	Strong (supports interfaces, generics, etc.)
Tooling	Basic	Advanced IDE support with autocompletion, refactoring

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1. Type Safety

JavaScript:

function greet(name) {
  return "Hello " + name;
}
greet(5); // Works, but may cause unexpected output

TypeScript:

function greet(name: string): string {
  return "Hello " + name;
}
greet(5); // ❌ Error: Argument of type 'number' is not assignable to parameter of type 'string'

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2. Interfaces and Type Checking

TypeScript Only:

interface Person {
  name: string;
  age: number;
}

function printPerson(p: Person) {
  console.log(p.name + " is " + p.age);
}

printPerson({ name: "John", age: 30 }); // ✅
printPerson({ name: "John" }); // ❌ Error: Property 'age' is missing

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3. ES6+ Features Compatibility

TypeScript: Supports latest ECMAScript features and compiles them to older JS versions:

const greet = (name: string = "Guest"): string => `Hello, ${name}`;

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4. Tooling and IntelliSense

TypeScript enables code suggestions, type inference, and error checking in editors like VS Code, improving developer productivity and reducing bugs.

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Conclusion:

TypeScript is a superset of JavaScript that adds optional static typing and advanced features for building large-scale applications with more safety and better tooling.