Chapter quiz · DOM & Platform APIs

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8 questions on DOM & Platform APIs. Pass 70% to clear the chapter.

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Quiz

DOM & Platform — Chapter Quiz

Eight questions on the DOM, events, forms, JSON, storage, regex, dates.

0/ 8

Question 1
1
Which call returns ALL elements matching a CSS selector?
Adocument.querySelector(".x")Bdocument.querySelectorAll(".x")Cdocument.getElementById(".x")Ddocument.findAll(".x")
querySelectorAll returns a NodeList of every match. querySelector returns only the FIRST match.
Question 2
2
Setting el.innerHTML to a string containing user input can introduce an XSS vulnerability.
TTrueFFalse
innerHTML parses the string as HTML, including <script> and onerror= handlers. Use textContent for user-supplied strings.
Question 3
3
Inside a submit listener, what stops the browser from navigating?
Ae.preventDefault()Be.stopPropagation()Creturn false from the listenerDe.cancel()
preventDefault cancels the browser's default action. stopPropagation only stops bubbling.
Question 4
4
What does this log?
```
localStorage.setItem("n", 5);
console.log(typeof localStorage.getItem("n"));
```
A"number"B"string"C"object"D"undefined"
localStorage stores everything as strings. The 5 was stringified on write. Use Number(...) when reading numbers back.
Question 5
5
What does this log?
```
const obj = { d: new Date("2026-01-01"), f: () => 1 };
console.log(Object.keys(JSON.parse(JSON.stringify(obj))));
```
A["d", "f"]B["d"]C["f"]D[]
Functions don't survive JSON serialization — they're dropped. Date becomes a string but the KEY survives. So only "d" remains.
Question 6
6
What does this log?
```
console.log(new Date(2026, 4, 11).getMonth());
```
A4B5C"May"D11
Date months are zero-indexed. May is 4 going in and 4 coming back. This is the most-bitten bug in Date.
Question 7
7
What does this log?
```
const m = "hi-123-bye".match(/-(\d+)-/);
console.log(m[1]);
```
A"-123-"B"123"C123Dnull
m[0] is the whole match ("-123-"); m[1] is the first capture group — the digits captured by (\d+).
Question 8
8
To attach a function to a button's click event, call button._________("click", handler).
addEventListener is the standard way to wire events. Older code may use button.onclick = ..., but addEventListener lets you attach multiple handlers and remove them cleanly.