JSFiddle - React, Tailwind, and code Playground

HTML

<input id="example">

<div id="output"></div>
<div id="o"></div>

JavaScript

function handler(e) {
    if (e.keyCode === 8) {
       return "0";
    }
     
}
var r = "";
var elem = document.getElementById("example");
elem.addEventListener("keydown", function (e) {
    this.keydownFired = true;
    r = handler.call(this, e);
    if (r=="0"){   document.getElementById("o").innerText = r;
               document.getElementById("o").style.backgroundColor = "lightgreen"; }
 
}, false)
elem.addEventListener("input", function (e) {
    if (!this.keydownFired) {
        e.keyCode = 8;
     handler.call(this, e);            
    }
    delete this.keydownFired;
 
}, false);