6.Code Written for the Next Person

The Problem in Real Life

Code That Works vs. Code Others Can Work With

Writing Clean, Reusable Code

• Naming: names should say what something is or does. t means nothing; ticket is clear. calc() is vague; calculateTotal() is clear. Booleans read best as questions: isStudent, hasPaid. JavaScript usually uses camelCase (totalCents), and fixed values often use CAPITALS (GROUP_SIZE). A good name removes the need for many comments.
• No magic numbers: a bare 0.8 in the middle of code makes the reader guess. A named constant — STUDENT_DISCOUNT = 0.8 — explains itself and can be changed in one place.
• Comments: notes in the code for people, ignored by the computer (// like this in JavaScript). The best comments explain why, not what — the code already shows what it does. // add 1 to count is useless. // students get the best price, so check them first is valuable.
• Formatting: consistent indentation, spacing and line breaks, so the structure is visible at a glance. Teams don't argue about this — they use an automatic formatter (like Prettier) that formats every file the same way on save.
• Reusable code: don't repeat yourself. If the same logic appears in two places, put it in one function and call it from both — exactly what Anna did with calculateTotal. This idea is often called DRY: Don't Repeat Yourself.
• Abstraction: hiding the details of how something works behind a simple name. The checkout page calls calculateTotal(cart, isStudent) and doesn't need to know how discounts work inside. Abstraction lets you use something without understanding all of it — like driving a car without knowing how the engine works.
• Modularity: splitting a program into separate, focused pieces — modules, usually separate files — that each do one thing. Pricing lives in pricing.js, email in email.js. One function should do one job, so calculateTotal shouldn't also send emails. Modules share code with export and import.

// pricing.js — every BlueTicket price is calculated here, and only here.

export const GROUP_SIZE = 5;
export const GROUP_DISCOUNT = 0.9;     // 10% off
export const STUDENT_DISCOUNT = 0.8;   // 20% off

export function calculateTotal(cart, isStudent) {
  const subtotalCents = sumTicketPrices(cart);

  // Students always get the best price, so check them first.
  if (isStudent) {
    return Math.round(subtotalCents * STUDENT_DISCOUNT);
  }
  if (cart.length >= GROUP_SIZE) {
    return Math.round(subtotalCents * GROUP_DISCOUNT);
  }
  return subtotalCents;
}

function sumTicketPrices(cart) {
  let totalCents = 0;
  for (const ticket of cart) {
    totalCents += ticket.priceCents;
  }
  return totalCents;
}

// checkout.js
// import { calculateTotal } from "./pricing.js";