Various tests for the hidden attribute. On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE". Tests that hidden in markup works: Tests that dynamically adding/removing hidden works: PASS - this line should appear Dynamic changing of hidden and effects on style: PASS getComputedStyle(test3, false).display is "none" test3.removeAttribute("hidden") PASS getComputedStyle(test3, false).display is "block" PASS getComputedStyle(test4, false).display is "block" test4.setAttribute("hidden", "") PASS getComputedStyle(test4, false).display is "none" PASS successfullyParsed is true TEST COMPLETE a