Tab through the parts, and a keyboard trap
Press Tab and then Enter: the buttons are real, so they work from the keyboard with no key code. The last two lines show a trap and its fix.
Every pointer action gets a keyboard twin: arrows turn, plus and minus zoom, Tab walks through the parts, Enter chooses. The canvas needs a way to take focus, a visible focus ring, and no keyboard trap.
Change the code and press Run (Ctrl+Enter). Predict what will happen first, then break it on purpose and read what changes. Your edits are saved and match the lesson page.
Ready for more? This phase has 4 hands-on exercises with automatic checks.
Practice questions
Write the code in the editor, run it, then open the model answer to compare.
Write a keydown handler for a container that handles ArrowUp and ArrowDown by changing state.tilt by 5 degrees, limited to −30 … 30, and leaves every other key alone.
Write the CSS so that a button shows a clear ring only for keyboard focus, not for mouse clicks.
Explain it without notes
Name the keyboard twin of: dragging, the mouse wheel, hover and a click.
Why must the key handler ignore events with Ctrl held, and why must it not call preventDefault() on Tab?
Console
Nothing logged yet.Expected console output
tab stops: bell -> saddle -> badge
selected: saddle
selected: nothing
selected: badge
handler that calls preventDefault on every key: TRAP: Tab is swallowed
handler that only takes arrow keys: Tab works