I’m just started using selectmenu and wanted to share how to control it. It’s not completely obvious to inexperienced jquery UI folks like myself…

Specifying a trigger function

First, we create the selectmenu UI widget from an existing <select> control, with the id=”selectmenu”.

$("#selectmenu").selectmenu({
  change: selectmenuChange
});

And selectmenuChange…
function selectmenuChange(event, value)
{
  switch(value.value)
  {
    case 0:
      alert('Hello!');
    break;
  }
  $("#selectmenu").selectmenu("value", "ignore"); // Put it back on the first option.
}

The last line should give you a clue as to what comes next.

Controlling the selectmenu after creation

$("#selectmenu").selectmenu("value", "ignore"); // Put it back on the first option.
$("#selectmenu").selectmenu("open"); // Open the selectmenu
$("#selectmenu").selectmenu("focus"); // Give it focus