TypeScript Essentials

TypeScript adds a static type system on top of JavaScript. Types catch bugs at compile time, improve editor support, and serve as living documentation. Whether you're adopting TypeScript for a new project or improving an existing codebase, understanding these essentials will make you productive and help you leverage the type system effectively.

Why TypeScript

TypeScript isn't "JavaScript with types"—it's a typed superset that compiles to JavaScript. The benefits compound as projects grow.

Benefits Over Plain JavaScript

Early error detection: Typos, wrong argument types, and missing properties surface in your editor and at build time instead of in production. A function expecting { id: number } will reject { id: "abc" } before the code runs.

Better tooling: Autocomplete, go-to-definition, and refactoring work reliably because the compiler knows the shape of your data. Rename a prop—TypeScript finds every usage.

Self-documenting code: Types describe function signatures, object shapes, and API contracts. New team members (and future you) understand interfaces without reading implementation.

Safer refactoring: Change a type and fix the resulting errors. The compiler guides you to every affected call site. Refactors that would be risky in JavaScript become routine.

Basic Types

TypeScript infers types when possible, but explicit annotations clarify intent and catch mistakes.

Primitives, Arrays, and Tuples

Primitives: string, number, boolean, null, undefined. Use them directly: let count: number = 0.

Arrays: string[] or Array<string> for homogeneous arrays. (string | number)[] for mixed. Prefer readonly for arrays you won't mutate.