Web Development Last-Minute Revision

30 quick revision notes for Web Development

1. Semantic tags like header, nav, main and footer improve accessibility and SEO compared with generic div wrappers.
2. defer scripts run after HTML parsing in order, while async scripts run as soon as they download in any order.
3. Always add width and height to images so the browser reserves space and avoids layout shift.
4. box-sizing: border-box makes width include padding and border, which keeps layouts predictable.
5. Specificity order is inline styles, then ids, then classes and attributes, then element selectors.
6. Flexbox is one-dimensional for rows or columns, while Grid controls rows and columns together.
7. rem is relative to the root font size, whereas em compounds based on the parent element's font size.
8. z-index only works within a stacking context, which transform, opacity and positioned elements can create.
9. let and const are block-scoped; var is function-scoped and hoisted with an initial value of undefined.
10. A closure is a function that keeps access to variables from the scope where it was created.
11. Microtasks such as promise callbacks run before macrotasks such as setTimeout callbacks in the event loop.
12. fetch does not reject on HTTP errors like 404 or 500, so always check response.ok before using data.
13. Event delegation uses one parent listener and event.target.closest to handle clicks on dynamic children.
14. Use textContent instead of innerHTML for user data to prevent cross-site scripting.
15. localStorage persists across sessions, sessionStorage clears when the tab closes, and cookies travel with every request.
16. Since PHP 8, comparing a number with a non-numeric string compares them as strings, so 0 == 'abc' is false.
17. Use password_hash and password_verify for passwords; never store plain text, md5 or sha1 hashes.
18. Call session_regenerate_id(true) after login to prevent session fixation attacks.
19. require stops the script with a fatal error if the file is missing, while include only raises a warning.
20. Prepared statements with PDO send SQL structure and data separately, which prevents SQL injection.
21. WHERE filters rows before grouping, while HAVING filters groups after GROUP BY using aggregates.
22. InnoDB is the default MySQL engine with transactions, row-level locks, foreign keys and crash recovery.
23. InnoDB's default isolation level is REPEATABLE READ, which gives each transaction a consistent snapshot.
24. Composite indexes follow the leftmost prefix rule, so column order in the index matters for queries.
25. Keyset pagination with WHERE id < last_id scales far better than large OFFSET values on big tables.
26. CSRF tokens plus SameSite cookies stop attackers from forging state-changing requests from other sites.
27. Broken access control, such as changing an id in the URL to see another user's data, is the top OWASP risk.
28. A, CNAME, MX and TXT records handle IP mapping, aliases, mail routing and verification data like SPF and DKIM.
29. A 502 Bad Gateway from Nginx usually means PHP-FPM or the upstream application is down or overloaded.
30. Lower DNS TTL a day before a server migration so the switch to the new IP spreads quickly.

Night-before checklist

• Revise your saved questions on this page once, aloud.
• Read the quick notes and mark any you cannot explain in one line.
• Rehearse a two-minute self-introduction and two project stories.
• Keep CV, ID, laptop charger and interview link ready; sleep on time.