lawofdemeter-5.js

const product = {
  id: 1,
  name: 'Supreme Vacuum Cleaner',
  quantity: {
    raw: '3',
    value: 3,
    validation: {
      isValid: true,
      errMessage: ""
    }
  },
  price: 100
}

const total = product.quantity.validation.isValid ? Number(product.quantity.value) * product.price : "$--"
const error = product.quantity.validation.isValid ? product.quantity.validation.errMessage : null