TypeScript

the intro

TypeScript is JavaScript with types. You describe the shape of your data once, and the compiler catches mistakes before the code runs — plus your editor gains autocomplete that actually knows your code. It compiles to plain JavaScript and has become the default for serious frontend work.

the sample

types catch bugs before runtime

type User = {
  name: string
  age: number
}

const u: User = { name: "Ericko", age: "oops" }
//        ~~~~ error: string is not number

the docs