# Shopping cart
Source: https://signy.dev/examples/shopping-cart/
Products, a cart and totals that follow every change.
The cart lives in a store. Changing a quantity writes one path, such as `cart.set('lines', 0, 'qty', 2)`, and only the cells that read it update. Computed values add up the subtotal, the discount and the total.
## Preview
[Open the page on its own](https://signy.dev/examples/shopping-cart/demo/index.html.md)
## Code
Save it as an `.html` file and open it in a browser. It loads Signy and Iris CSS from the CDN, so there is nothing to install or build.
**Show the full page**
```html
Shopping cart - Signy example
```
## What it uses
- [Store](https://signy.dev/documentation/1/reactivity/store/index.html.md) with path writes
- [Computed](https://signy.dev/documentation/1/reactivity/computed/index.html.md) totals
- [For](https://signy.dev/documentation/1/templates/for-and-index/index.html.md) and [Show](https://signy.dev/documentation/1/templates/show/index.html.md)