code: function onChange (menu, setLabel) {
    var dropdown = menu.parent(".dropdown");
  
    // Don't auto-close the menu when items are clicked
    menu.find("a").on("click", function (event) {
      event.stopPropagation();
    });
  
    // Set the label immediately, and again whenever the menu is closed
    setLabel();
    dropdown.on("hidden.bs.dropdown", setLabel);
  
    // Track when a dropdown menu is shown
    dropdown.on("shown.bs.dropdown", function () {
      analytics.trackEvent("options", "shown", menu.attr("id"));
    });
  }
docs: Calls the given function whenever the user selects (or deselects)
  a value in the given drop-down menu.
  
  @param {jQuery} menu
  @param {function} setLabel