Apa bedane antarane null lan undefined?

Question

IT Interview Practice · Accepted Answer

Loro-lorone mewakili "ora ana nilai," nanging kanthi **niat lan asal usul" sing beda.

- **`undefined`**: ang *kaantanan* saka nilai, biasane disetel dening JavaScript engine — variabel sing kadhaptar-nanging ora ditugasake, properti obyek sing ilang, parameter fungsi sing ora sampeyan terusake, utawa fungsi tanpa `return`.
- **`null`**: nilai "kosong" *sengaja* sing **sampeyan** tugasake kanggo ngomong "ora ana apa-apa ing kene kanthi niyat."

```js
let a;                 // undefined — declared, not assigned
const obj = {};
obj.missing;           // undefined — property doesn't exist
function f() {}
f();                   // undefined — no return

const b = null;        // null — you chose to empty it
```

## Comparisons

```js
null == undefined;   // true  — loose equality treats them as equal
null === undefined;  // false — different types
typeof undefined;    // "undefined"
typeof null;         // "object"  (historical bug)
```

## Practical handling

```js
const value = input ?? "default"; // defaults on EITHER null or undefined
user?.address?.city;               // optional chaining — undefined if any link is null/undefined
```

## Napa iku penting

Gunakake **`null`** kanggo ngendhaki nilai kanthi niyat (cth. "ora ana pangguna sing dipilih"), lan gatekake **`undefined`** minangka "durung disetel". Operator `??` (nullish coalescing) lan `?.` (optional chaining) nangani loro-lorone sajeroning setunggal, mula iku panyaranane luwih akeh digunakake.

Comparisons

Practical handling

Napa iku penting

Pitakon sing gegandhengan