use Upline\ComputedField;

ComputedField::make('Total')
    ->setComputedFunction(function ($data) {
        return $data['price'] * $data['quantity'];
    })
    ->setSourceFields(['price', 'quantity'])

Explanation

->setSourceFields($fields) method sets fields that will be watched for changes, and will be sent to compute the field value.

->setComputedFunction(...) method sets a function that will be called to calculate a value of the field.

To be done

Add image/video of component to readme
Test on nova 4
Add tests
Add details and/or index view
Discover ability to use laravel dynamic attributes functions