You were almost there -
import $ from "jquery";
$(document).ready(function(){
$("#root").click(function(){
const buttonText = rootApp.innerHTML;
if (buttonText === 'ON'){
rootApp.innerHTML = 'OFF';
} else {
rootApp.innerHTML = 'ON';
}
})
})
const rootApp = document.getElementById("root");
rootApp.innerHTML = 'ON';