Move Statements into Function

Goal

Setup or follow-up that happens around every call to a function moves inside the function, so the caller's contract shrinks.

Before the refactoring

log('start fetch');
const data  = fetch(url);
log('start fetch');
const data2 = fetch(url2);

After the refactoring

function fetchLogged(url) {
  log('start fetch');
  return fetch(url);
}

Savings

One fewer thing to remember at the call site; consistency is enforced by the function's definition, not by convention.

Note

If the moved statements aren't always wanted, the function grows a flag argument — verify every caller really needs the moved behavior.