8.2

function withBoxUnlocked(body) {

  var closed = box.locked;
  if (!closed) return body();
  box.unlock();
  try{ 
    return body();
  } finally{
    box.lock();
  }
}
withBoxUnlocked(function() {
  box.content.push("gold piece");
});

try {
  withBoxUnlocked(function() {
    throw new Error("Pirates on the horizon! Abort!");
  });
} catch (e) {
  console.log("Error raised:", e);
}

console.log(box.locked);
// → true