concatinating and combining 2 variable

i wanna join two variable that selected by select box with each other i mean i wanna have : "-somthing" or "+somthing"

        var FilterList ={ 
        sort_by : ""
    }


    
        sort.addEventListener( 'change' , ()=>{
        var value = sort.value;
        var text = sort.options[sort.selectedIndex].value;
        FilterList.sort_by = text
        

        })

        
        sortKind.addEventListener( 'change' , ()=>{
        var value = sortKind.value;
        var text2 = sortKind.options[sortKind.selectedIndex].value;
        FilterList.sort_by = text2
        
    })