JSFiddle - React, Tailwind, and code Playground

HTML

<input type="range" id="in" min="0" max="10000" step="1">
<output id="out"></output>

CSS

output {
  border: 1px solid silver;
  width: 5em;
  margin-left: 1em;
  display: inline-block;
}

JavaScript

var inElement = document.querySelector('#in');
var outElement = document.querySelector('#out');
outElement.value = inElement.value;

inElement.addEventListener('input', function(event) {
 	outElement.value = f(inElement.value);
});

function f(x) {
  return x;
}