Extract Function

function priceOrder(order: Order): Money {
  const a = priceOrderPart1(order)
  const b = priceOrderPart2(order, a)
  return priceOrderPart3(order, a, b)
}

function priceOrderPart2(
  order: Order, subtotal: Money,
): Money { ... }

// To know what happens, you open all three.
// The parameters carry the sequence that the
// original code carried by being in order.

function priceOrder(order: Order): Money {
  const subtotal = sumLineItems(order.items)
  const discount = bestApplicableDiscount(order)
  const taxable = subtotal.minus(discount)
  return taxable.plus(vatFor(order.shipTo, taxable))
}

// Each name is a thing the finance team says out
// loud. The function now reads as the definition
// of what an order costs.

The right-hand version is not better because it is shorter — both are four lines. It is better because each name is a concept that exists in the business, which means a change to "how discounts are chosen" has an obvious address, and a reader who only needs to know the order of operations never has to open anything. The left-hand version has the same line count and none of that: the names carry no information, so every question requires opening every function, and the parameter chaining has made the sequence explicit in the worst possible place (Naming and Domain Language).

1// the extraction that says "wrong seam"
2function applyAdjustments(
3  subtotal: Money, customer: Customer, region: Region,
4  promos: Promo[], now: Date, isRetry: boolean,
5): Money { ... }
6 
7// six parameters, one of them a boolean flag,
8// one of them a clock. The block was not separable.
9 
10// what it was telling you
11class OrderPricing {
12  constructor(private readonly clock: Clock,
13              private readonly promos: PromoCatalog) {}
14 
15  adjust(subtotal: Money, order: Order): Money { ... }
16}

The boolean is the loudest signal — isRetry means the function does two things and the caller picks which (Boolean Parameters). The now: Date says the block depends on time and nobody decided where that dependency lives (Time as a Dependency). Six parameters was not a style problem to be fixed by bundling them; it was the code declining to be a function.