Chapter quiz · Control Flow

Test what you learned.

8 questions on Control Flow. Pass 70% to clear the chapter.

← Review chapter lessons

Quiz

Control Flow — Chapter Quiz

Eight questions on comparisons, conditionals, and loops.

0/ 8

Question 1
1
What does this code log?
```
console.log(0 == false);
```
AtrueBfalseCTypeErrorDNaN
Loose equality (==) converts types. 0 and false both coerce to the same value. This is exactly why === is preferred.
Question 2
2
Which operator falls back **only** when the value is null or undefined?
A||B??C&&D?.
?? (nullish coalescing) falls back only on null or undefined. || falls back on any falsy value (including 0, "", false).
Question 3
3
What does this code log?
```
const user = null;
console.log(user?.name ?? "guest");
```
AnullBundefinedC"guest"DTypeError
user?.name short-circuits to undefined (no crash). Then ?? sees undefined and falls back to "guest".
Question 4
4
Inside a forEach callback, what does break do?
AExits the loop earlyBSkips to the next itemCSyntaxError — break only works in real loopsDReturns from the callback
forEach runs a callback for each item — there's no loop to break out of. The parser throws SyntaxError. If you need early exit, use for..of instead.
Question 5
5
Which loop iterates the **values** of an array, string, set, or map?
Afor..inBfor..ofCwhileDClassic for (let i = 0; i < n; i++)
for..of iterates values of any iterable. for..in iterates property names (keys) of an object — easy to confuse, different job.
Question 6
6
A switch block needs break after every case — forgetting it lets execution fall through to the next case.
TTrueFFalse
Yes — switch falls through unless you break. Sometimes fall-through is intentional (grouping cases), but most of the time forgetting break is a bug.
Question 7
7
What does this code log?
```
const numbers = [3, 7, 12, 4];
for (const n of numbers) {
  if (n > 10) {
    console.log(n);
    break;
  }
}
```
A12B12 then 4C3 7 12DNothing
The loop finds 12 > 10, logs it, and breaks out of the loop. 4 is never reached.
Question 8
8
To safely read user.address.city when user or address might be missing, use user_____.city.
user?.address?.city — ?. between each level returns undefined instead of crashing if any link is null or undefined.