index.js

var slideIndex = 0;
showSlides();

function showSlides() {
  
    var slides = document.getElementsByClassName("slideBanner");
    var dots = document.getElementsByClassName("dot");
    for (i = 0; i < slides.length; i++) {
      slides[i].style.display = "none";  
    }
    slideIndex++;
    if (slideIndex > slides.length) {slideIndex = 1}    
    for (i = 0; i < dots.length; i++) {
        dots[i].className = dots[i].className.replace(" active", "");
    }
    slides[slideIndex-1].style.display = "block";  
    dots[slideIndex-1].className += " active";
    setTimeout(showSlides, 5000);
}

function buttonFunc (){
    let x, text;
    x = document.getElementById("numb").value;

    if ( x.length == 0) {
        text = "mohon isi data dengan lengkap";
    } 
    document.getElementById("demo").innerHTML = text;
}