selectAllButton
defines whether the Select All button should be shown
selectAllButton?: boolean;
Example
var combo = new dhx.Combobox("combo_container", {
// enables multiple selection of options
multiselection:true,
// shows the Select All button
selectAllButton: true
});
Related sample: Combobox. Select All Button
note
To be able to select several options you need to enable the multiselection option.