Middle click

The wheel is a button, and pressing it means something specific in every desktop browser. On a link it opens the destination in a new tab without leaving the page, which is the whole point: a reader working through a list of results collects the interesting ones and keeps their place. On a tab it closes that tab. On empty page background it starts autoscroll, the mode where the page keeps scrolling in whatever direction the pointer is held from the anchor. Three jobs, one button, and none of them announced anywhere in the interface.

In the DOM this is auxclick, an event browsers introduced precisely so that middle and back and forward presses stopped arriving as click. A handler reads event.button, where 0 is primary, 1 is the wheel, and 2 is the one that raises the secondary click menu. Two details bite. The browser’s own middle-click behaviour is attached to a real anchor with a real href, so a link built as a div with a click handler has no middle-click behaviour at all, and no amount of auxclick code gives it back the browser’s own tab handling. And on Windows and Linux a middle press on the page starts autoscroll unless the mousedown is cancelled, which is why a page that wants to handle the button itself has to say so at press time rather than at click time.

Web applications forget it constantly, and the failure is always the same shape. A results list, a file tree, or a message list is built out of clickable rows rather than links, so middle-clicking a row does nothing, and every reader who has ever collected tabs from a list of results discovers that this particular list refuses to. The fix is not more JavaScript: it is to render the thing that navigates as an anchor with an href, let the browser handle the modifiers and the wheel press, and add behaviour on top. That single change also buys Ctrl-click and Cmd-click, drag to bookmark, copy link address, and open in a new window, all of which are the same affordance seen from different angles.

None of this makes the button safe to depend on. Trackpads mostly have no middle button, tablets and phones have none at all, and assistive setups may remap it, so a wheel press can only ever be a shortcut for something reachable another way. Linux adds a fourth convention that surprises everyone who meets it, pasting the primary selection wherever the wheel is pressed, which is worth knowing about mostly because it explains stray text appearing in a field nobody typed into.