X'inhuma l-union u l-intersection types?

Question

IT Interview Practice · Accepted Answer

A **union** (`A | B`) tfisser "jew A **jew** B." An **intersection** (`A & B`) tfisser "kemm A **u** B fl-istess ħin."

```ts
// Union — value is one of several types
type Status = "loading" | "success" | "error"; // string literal union
let s: Status = "loading"; // only these three allowed

function id(x: string | number) { /* x is string OR number */ }
```

## Jaħdem mal-unions: tista' tuża biss dak li huwa komuni

```ts
function format(x: string | number) {
  // x.toFixed(2); // ❌ toFixed doesn't exist on string
  if (typeof x === "number") return x.toFixed(2); // ✅ narrowed to number
  return x.toUpperCase();                          // ✅ here it's a string
}
```

Sa sa tkun **narrow** union, tista' taċċessa biss l-membri preżenti fuq *kull* membru tal-union — il-compiler jipproteġilek.

## Intersection — ikkombina l-forom

```ts
type Name = { name: string };
type Age = { age: number };
type Person = Name & Age; // must have BOTH name and age

const p: Person = { name: "Ann", age: 30 }; // both required
```

L-Intersections huma kbira għat-tqassim/taħlit ta' tipi ta' oġġetti (eż. iżżid props għal tip eżistenti).

## Għalfejn dan importanti

Unions jimmudellaw "waħda minn diversi possibbiltajiet" — il-bażi ta' mudellazzjoni tas-stat sigura (eż. discriminated unions għal reducer state), overloads ta' funzjoni, u tipi nullable (`T | null`).

L-Intersections jikkombinaw tipi flimkien.

Flimkien jagħmluha s-sistema ta' tipi TypeScript espressiva biżżejjed biex tirrifletti d-data reali b'eżattezza.

Jaħdem mal-unions: tista' tuża biss dak li huwa komuni

Intersection — ikkombina l-forom

Għalfejn dan importanti

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