TypeScript: `unknown`, `any` и `never` — пример кода

// any — contagious, unsafe, silent
const a: any = JSON.parse('{}');
a.foo.bar.baz();      // ✅ compiles, ❌ crashes — no checking at all
const n: number = a;  // any flows into number with no error

// unknown — safe top type; must narrow before use
const u: unknown = JSON.parse('{}');
// u.foo;             // ❌ Error: object is of type 'unknown'
if (typeof u === 'object' && u && 'foo' in u) {
  (u as { foo: unknown }).foo; // ✅ only after narrowing
}

// never — the bottom type
function fail(msg: string): never { throw new Error(msg); } // never returns
type T = string | never;   // = string  (never disappears from unions)

// never powers exhaustiveness
type Dir = 'up' | 'down';
function move(d: Dir) {
  switch (d) {
    case 'up':   return 1;
    case 'down': return -1;
    default: const _: never = d; return _; // errors if a new Dir is added
  }
}

// catch clauses are `unknown` (with useUnknownInCatchVariables/strict) — not `any`
try { /* ... */ } catch (e) {
  // e.message; // ❌ e is unknown
  if (e instanceof Error) console.log(e.message); // ✅ narrow first
}