JSFiddle - React, Tailwind, and code Playground

by Roko

HTML

JS<input type="text" class="form-control js_leading_zero" placeholder="000000" maxlength="6">

JavaScript

const inputField = document.querySelector('.js_leading_zero')

inputField.addEventListener('blur', updateInput);
inputField.addEventListener('focus', clearInput);

function updateInput() {
  if (inputField.value.length) {
    inputField.value = inputField.value.padStart(6, '0');
    inputField.placeholder = inputField.value;
  } else {
    inputField.value = inputField.placeholder;
  }
}

function clearInput() {
   inputField.value = "";
}