# computed() & effect() — Angular

Source: https://www.geekswithgeeks.com/en/angular/ng-computed-effect

> Derive values from signals and run side effects when they change.

## computed()

`computed()` derives a read-only signal from others — it recalculates automatically only when a dependency changes.

```typescript
import { signal, computed } from '@angular/core';

export class CartComponent {
  price = signal(250);
  quantity = signal(2);
  total = computed(() => this.price() * this.quantity());
}
```

## effect()

`effect()` runs a side effect (logging, localStorage, analytics) automatically whenever the signals it reads change.

```typescript
import { effect } from '@angular/core';

constructor() {
  effect(() => {
    console.log('Total is now', this.total());
  });
}
```

## computed vs effect

Use `computed()` when you need a **value** back; use `effect()` when you just need to **do** something (no return value) as a reaction.