unknown เทียบกับ any: ตัวเลือกที่ปลอดภัยกว่า

let val: any = getData();
val.someMethod(); // TypeScript: OK. Runtime: possible crash

let val: unknown = getData();
// val.someMethod(); // Error: Object is of type 'unknown'

let input: unknown = getInput();
if (typeof input === 'string') {
  console.log(input.toUpperCase()); // OK — narrowed to string
}

let x: unknown = 'hello';
// let s: string = x; // Error
let s: string = x as string; // OK with assertion

try {
  doSomething();
} catch (err: unknown) {
  if (err instanceof Error) {
    console.log(err.message); // safe
  }
}

const raw: unknown = JSON.parse(text);
if (
  typeof raw === 'object' &&
  raw !== null &&
  'name' in raw
) {
  console.log((raw as any).name);
}

function isUser(val: unknown): val is { name: string } {
  return typeof val === 'object' && val !== null && 'name' in val;
}

// unknown: anything can be assigned to it
let a: unknown = 42; // OK

// never: nothing can be assigned to it
function fail(): never { throw new Error(); }

import { z } from 'zod';
const UserSchema = z.object({ name: z.string(), age: z.number() });
const user = UserSchema.parse(unknownData); // throws if invalid