util.js

function getSingleElementByClassName(className) {
  return document.getElementsByClassName(className)[0];
}

function replaceInnerInClass(className, text) {
  var theClass = getSingleElementByClassName(className);
  theClass.innerHTML = '';
  theClass.appendChild(document.createTextNode(text));
}

function appendTextToClass(className, text) {
  getSingleElementByClassName(className).appendChild(document.createTextNode(text));
}

function replaceTextInClass(className, text) {
  replaceInnerInClass(className, '');
  appendTextToClass(className, text);
}