Android-style Scroller With Section Indexing

This is a dynamic vertical scroller with section indexing feature, written in JavaScript and CSS. Great for contact list.

Similar to the Android & Material Design RecyclerView that displays an alphabets bubble following the scrollbar.

How to use it:

Create the HTML for the scroller.

<div id="container" class="hideText">
  <div id="scroll-display">
  </div>
  <ul id="list">
  </ul>
</div>

Prepare your data to be presented in the scroller.

var aNames = [
    {
      name: "Kamal"
    },
    {
      name: "Perry"
    },
    {
      name: "Ishmael"
    },
    // ...
]

The main JavaScript to activate the scroller.

// Sorting names
aNames = aNames.sort(function(oName1, oName2) {
  return oName1.name > oName2.name ? 1 : -1;
});
// Make rows
var oList = document.querySelector("#list");
for (var iIndex = 0; iIndex < 100; iIndex++) {
  var oItem = document.createElement("li");
  oItem.innerText = aNames[iIndex].name;
  oList.appendChild(oItem);
}
var iItemHeight = 40;
// Caching children
var aChildren = oList.querySelectorAll("li");
var oDisplay = document.querySelector("#scroll-display");
var oContainer = document.querySelector("#container");
var hideFn = null;
 
oList.addEventListener("scroll", function() {
  oContainer.classList.remove("hideText");
  var iScrollTop = oList.scrollTop;
  var iScrollHeight = oList.scrollHeight;
  var iHeight = oList.clientHeight;
  var currentItem = Math.floor(iScrollTop / iItemHeight);
  oDisplay.setAttribute("data-value", aChildren[currentItem].innerText.charAt(0));
  oDisplay.style.transform = `translateY(${( (iScrollTop * iHeight) / iScrollHeight)}px)`;
  
  // Debounce hiding 
  if(hideFn){
    clearTimeout(hideFn);  
  }
  hideFn = setTimeout(function() {
    oContainer.classList.add("hideText");
  }, 200);
});

The example CSS.

#list {
  height: 300px;
  display: flex;
  flex-direction: column;
  list-style: none;
  padding-left: 0px;
  margin: 0px;
  overflow-y: auto;
}
#list li {
  background: white;
  padding: 10px 20px;
  margin: 2px;
}
#scroll-display {
  position: relative;
  will-change: transform;
}
#scroll-display:after {
  border-radius: 30px;
  width: 15px;
  text-align: center;
  height: 15px;
  content: attr(data-value);
  position: absolute;
  top: 0;
  right: 20px;
  background: rgba(0, 0, 0, 0.7);
  color: white;
  padding: 10px;
  font-family: Courier;
}
#container.hideText #scroll-display { display: none; }