With jquery:

$('.kk').keyup(function(e){
    var t=$(this);
    if(e.keyCode!=8){   
        let val=t.val();
        val =val.replace(/(\d{4}(?!\s))/g, "$1 ");
        if(val.length==20){
            val=val.trim()
        }
        t.val(val);
    }
})

Thanks to @thefourtheye