TypeScript - Introduction

What is TypeScript?

TypeScript (TS) is a superscript of JavaScript that adds a static type system and powerful tooling. It compiles to plain JavaScript, so it runs everywhere JS runs: browsers, Node.js, Deno, Bun, and edge runtimes.

Why TypeScript?

• Fewer bugs: Types catch mistakes before runtime.
• Better IDE help: IntelliSense, refactoring, and auto-complete are dramatically better.
• Clarity at scale: Types become living documentation across teams.

Course Outcomes

• Understand and use all core and advanced TS features confidently.
• Design ergonomic public APIs and .d.ts declaration files.
• Build Node services and frontends with robust types, tests, and tooling.

How TS fits into your workflow

1. You write .ts (and optionally .tsx for JSX).
2. The compiler/transpiler emits JavaScript that your runtime understands.
3. Editors use types to power navigation, rename, and inline docs.

Example: Plain JS vs TypeScript

// JavaScript
function add(a, b) { return a + b }

// TypeScript
function addTs(a: number, b: number): number { return a + b }

// Compile-time checks prevent bad calls:
// addTs("1", 2) // Error: Argument of type 'string' is not assignable to 'number'

What you'll learn next

• Install TS and compile your first program
• Master the type system: primitives, unions, generics, narrowing, and more
• Real-world tsconfig, build tools, tests, and publishing types