Long Function

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Symptom

Functions whose body has dozens of lines and a mix of concerns — fetching, calculating, formatting, and logging all interwoven.

Goal

Each function reads as a sequence of named single-responsibility steps; nothing does more than its name advertises.

Smellier version

function ship(order) {
  if (!order.id) throw new Error('missing id');
  const tax = order.total * 0.1;
  const grand = order.total + tax;
  email(order.user, `Total ${grand}`);
  log(order);
}

Fresher version

function ship(order) {
  validate(order);
  const grand = withTax(order);
  notify(order, grand);
}

Savings

Faster to read, easier to test, simpler to change one step without touching the others.

Note

Each line is an opportunity for the reader to lose context; understanding requires holding the whole function in working memory.