What is the satisfies operator?

type Colors = Record<string, string | number[]>;

// With type annotation - loses specificity
const colors1: Colors = {
  red: "#ff0000",
  green: [0, 255, 0]
};
colors1.red.toUpperCase(); // Error: might be array

// With satisfies - keeps specific types
const colors2 = {
  red: "#ff0000",
  green: [0, 255, 0]
} satisfies Colors;

colors2.red.toUpperCase();  // OK: knows it's string
colors2.green.map(n => n);  // OK: knows it's array

type Route = { path: string; element: string };

// Type annotation
const route1: Route = { path: "/", element: "Home" };
route1.path; // type: string

// satisfies
const route2 = { path: "/", element: "Home" } satisfies Route;
route2.path; // type: "/" (literal)

// Validate object keys exist
type ValidKeys = "name" | "age";

const config = {
  name: "John",
  age: 30
} satisfies Record<ValidKeys, unknown>;