Hard Frontend Developer questions

32 questions · 20 points each for a correct first answer.

1. 1.Cause of a hydration mismatchreact, ssr, hydrationhard
2. 2.Avoiding layout thrashingweb-performance, renderinghard
3. 3.Race condition in data fetchingreact-hooks, asynchard
4. 4.Why React.memo did not helpreact, performancehard
5. 5.z-index that does not workcss, stacking-contexthard
6. 6.Preventing XSS from user HTMLweb-security, xsshard
7. 7.Reducing the initial bundleweb-performance, bundlinghard
8. 8.Losing this when a method is extractedjavascript, this-bindinghard
9. 9.Ellipsis that never truncates in Flexboxflexbox, css, debugginghard
10. 10.Every context consumer re-rendersreact-context, react-performancehard
11. 11.Effect that fetches foreverreact-hooks, debugginghard
12. 12.Tooltip flashes in the wrong placereact-hooks, renderinghard
13. 13.Janky slide-in animationweb-performance, css-animationshard
14. 14.Order of logs around awaitevent-loop, async-javascripthard
15. 15.Order of object keysjavascript, objectshard
16. 16.map with parseIntjavascript, arrayshard
17. 17.A CSP that stops injected scriptsweb-security, content-security-policyhard
18. 18.CSRF risk left with SameSite=Laxweb-security, csrfhard
19. 19.Unsafe postMessage listenerweb-security, browser-apishard
20. 20.Slow click handler hurts INPcore-web-vitals, web-performancehard
21. 21.Layout shift when the web font loadsweb-fonts, core-web-vitalshard
22. 22.Old version after deploy with a service workerservice-workers, cachinghard
23. 23.Typing lags while a big list filtersreact-concurrency, react-performancehard
24. 24.Optimistic like button done rightstate-management, ux-patternshard
25. 25.Memory grows in a single-page appmemory-leaks, devtoolshard
26. 26.Importing one function pulls a whole librarybundlers, web-performancehard
27. 27.Cascade layers versus specificitycss, css-cascadehard
28. 28.Card layout based on its own widthcss, responsive-designhard
29. 29.Exhaustive check with nevertypescripthard
30. 30.When extra properties are an errortypescripthard
31. 31.Status message screen readers missaccessibility, ariahard
32. 32.Comparator that returns a booleanjavascript, arrays, debugginghard