JSFiddle - React, Tailwind, and code Playground

HTML

input:<input id="input" type="number" onkeyup="myFunction()"/>
answer:<input id="answer" type="text" value=""/>

JavaScript

function myFunction() {
  var inputVal = document.getElementById("input").value;
  var answerVal = document.getElementById("answer");
  var percentage = (0.0015/100) * parseInt(inputVal,10) * 100;
  console.log(inputVal, typeof inputVal);
  if(inputVal !== ''){
     answerVal.value = percentage;
  }else{
  answerVal.value = '';
  }
}