← Your Timer Doesn't Know You Tabbed AwayQuiz
Page Visibility API
Check what actually stuck about visibilitychange, document.hidden, and why it beats window blur/focus for detecting whether anyone can see the page.
questions7
pass mark70%
resultsat the end
No account needed. Answer all 7 questions, then see your score with every answer explained and a reference to the spec or MDN — pass and you can claim a certificate.