JavaScript Practice 18/21

Fix the bug: one user's edit changes everyone

Every new user starts from one defaultSettings object, spread into a fresh object of their own. That is the ordinary way to do this, and the code below runs without a single error.

Then read the output. Ana changed her own settings. Ben never opened his - and Ben's email notifications are off.

The strange part is what did work. Ana switched to the dark theme and Ben is still on light, so the copy is clearly doing something. Out of the same object, through the same spread, one field isolated correctly and one field leaked.

That split is the entire bug. It is also not a bug in JavaScript - it is the spread operator doing exactly what it promises, no more.

Your task: fix makeUserSettings(name) so each user owns their settings outright. Changing one user's notifications must not change another user's, and must not change defaultSettings for whoever signs up next.

You'll practice:

Reading a plausible output as a claim, then checking whether the claim is true
Finding where a copy stopped, and copying the level it stopped at

// Each user gets a copy of the defaults. This runs fine - read the output.
// Ben never opened his settings.
const defaultSettings = {
  theme: "light",
  notifications: { email: true, sms: false },
};

function makeUserSettings(name) {
  return { name, ...defaultSettings };
}

const ana = makeUserSettings("Ana");
const ben = makeUserSettings("Ben");

// Ana changes two of her own settings.
ana.theme = "dark";
ana.notifications.email = false;

console.log("Ben's theme:", ben.theme);               // expected: light
console.log("Ben's email:", ben.notifications.email); // expected: true