Collapse/expand the WhatsApp Web icon rail AND the chat list with clickable carets (chat-list caret on by default; falls back to hover show/hide when disabled), plus a draggable handle to resize the chat list width.
Reclaim screen space in WhatsApp Web by collapsing the parts you don't need.
Adds two small carets to the left edge of WhatsApp Web:
Both panels slide away when collapsed, giving the open conversation the full width. Click a caret again to bring its panel back. Your collapsed/expanded choices are remembered between visits.
You can also drag the right edge of the chat list to resize how wide it is.
That's it — it works automatically on web.whatsapp.com after install.
By default the chat list is controlled by its caret. If you'd rather have the chat list reveal automatically when you move your mouse to the left edge of the screen, open the script and set:
const USE_CHATLIST_CARET = false;
The chat-list caret then disappears and the chat list shows on hover (with a short grace period so it doesn't vanish the instant you move away).