Part 1.1Course introduction

TypeScript is JavaScript with a type system. You write familiar JavaScript, then TypeScript checks your assumptions before the program runs and produces ordinary JavaScript for browsers, Node.js and other JavaScript environments.

What TypeScript is

TypeScript does not replace JavaScript: every valid JavaScript program is also valid TypeScript. Its value is that you can describe the shape of data, document intent directly in code and discover many mistakes while writing rather than testing an application.

function greet(name: string): string {
  return `Hello, ${name}`;
}

greet("Jamie");

The annotations disappear when the code is compiled. The browser receives JavaScript, while you receive useful editor feedback and compile-time checks.

This course

This course assumes basic JavaScript knowledge. Start by compiling a small file, then build from simple annotations through interfaces, generics, classes, browser APIs and production configuration. Each lesson focuses on when a feature helps, not merely how to spell it.

Keep a small project alongside the lessons. TypeScript becomes natural once you use it to model data you genuinely care about.