Semantic UI: Multi Select Dropdown pre-select values

Add values ( <option selected="selected"> ) dropdown semantic about all select :

$("select").each(function(){
            var $that = $(this);
            var values = $that.val();
            $("option", $that).each(function(){
                $(this).removeAttr("selected");
            });
            $that.dropdown('set selected', values);
            $("option", $that).each(function(){
                var curr_value = $(this).val();
                for(var i = 0; i < values; i++){
                    if(values[i] == curr_value){
                        $(this).attr('selected','selected');
                    }
                }
            });
        });

Your syntax is slightly off. Try this:

$('.ui.fluid.dropdown').dropdown('set selected',['Role1','Role2']);