Menene bambanci tsakanin null da undefined?

Question

Accepted Answer

Dukansu suna wakilar "ba da daraja," amma tare da **manufa da asali daban-daban**.

- **`undefined`**: rashin **daraja**, galibi sada ta injin JavaScript — mai juna-amma-ba a sanya, kadarar aiki ta rashin amfani, sigina ba ka jamawa, ko aiki ba tare da `return`.
- **`null`**: daraja "gudu" **da kai** ke sanya don cewa "ni ba tare da wani abu nan."

```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
```

## Daidaitawa

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

## Taƙaicin aiki

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

## Menene mahimmancin haka

Sanya **`null`** don cire daraja baki-waje (m.s. "babu mai amfani da zaɓu"), kuma dauki **`undefined`** a matsayin "har yanzu ba a sanya." Ƙwaloyin `??` (nullish coalescing) da `?.` (optional chaining) suna sarrafa duka biyu a jiya gida, wanda shine dalilin da yasa suke ta da amfani sosai.