Lesson 1: Why TypeScript? The Case for Types

JavaScript is dynamically typed, which is great for quick scripts but painful at scale. TypeScript adds a static type layer on top of JavaScript that catches bugs before you run your code.

What you get

• Autocomplete that actually knows your data shapes
• Compile-time errors instead of runtime surprises
• Self-documenting function signatures
• Safe refactoring across large codebases

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

greet(42); // ❌ Error: number is not assignable to string

TypeScript compiles down to plain JavaScript, so it runs anywhere JS runs — the browser, Node, Deno, or a static site like this one.