TypeScript is JavaScript with types. You declare what kind of data each variable holds, and the compiler catches mistakes before your code runs. In 2026, it's the default for React, Next.js, and every AI app builder. Here's how to start.
Why types matter
Without types, a function that expects a number silently receives a string, and the bug shows up at 2am in production. With types, the editor catches it as you type. TypeScript doesn't prevent all bugs — it prevents the dumb ones, which are the majority.
The basics (5-minute version)
- Primitive types:
string,number,boolean,null,undefined - Arrays:
string[]orArray<string> - Objects:
interface User { name: string; age: number } - Functions:
function greet(name: string): string - Union types:
string | number— accepts either - Optional:
name?: string— may be undefined
TypeScript in React
- Props:
interface Props { title: string; count: number } - State:
const [count, setCount] = useState<number>(0) - Events:
onClick: (e: React.MouseEvent) => void - Children:
{ children: React.ReactNode }
Getting started
If you're using Next.js (or InBuild's exported code), TypeScript is already configured. Files use .tsx extensions. The compiler runs automatically during development and build. Start writing types for your interfaces and props — the editor autocomplete will immediately improve.
The practical advice
Don't type everything on day one. Start with function parameters and return types. Add interface definitions for your data models. Let the compiler guide you — when it shows a red squiggly, read the error message. TypeScript error messages are verbose but accurate. Within a week, you'll wonder how you wrote JavaScript without it.