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                <h2>MutationObserver Example - characterData</h2>

<p>This page uses the MutationObserver API to watch for changes to the DOM tree. In this case, the MutationObserver is looking for character data changes on the targeted element.</p>

<p> A "Start..." and a "Stop..." button are used to start and stop the MutationObserver. Console messages are displayed specifying which change took place and whether the MutationObserver is started or stopped.</p>

<p id="field" contenteditable="true" tabindex="0" class="f">Edit this text!</p>

<button class="btnStart">Start Observing for Mutations</button> 
<button class="btnStop" disabled>Stop Observing for Mutations</button>



                body {
  padding: 0 20px;
  font-size: 1.2em;

.f {
  border: dashed 3px #aaa;
  padding: 10px;
  font-size: 20px;

button {
  margin: 3px;


                let btnStart = document.querySelector('.btnStart'),
    btnStop = document.querySelector('.btnStop'),
    field = document.getElementById('field'),
    options = {
      characterData: true
    observer = new MutationObserver(mCallback);

function mCallback(mutations) {
  for (let mutation of mutations) {
    if (mutation.type === 'characterData') {
      console.log('Mutation Detected: Character data has been altered.');

function doFieldInput() {
  field.addEventListener('input', function () {
    if (!field.childNodes[0]) {;
  }, false);

function doLogAndBtn(msg) {
  btnStart.disabled = !btnStart.disabled;
  btnStop.disabled = !btnStop.disabled;

field.addEventListener('blur', function() {
  if (!field.childNodes[0]) {
    field.innerHTML = 'Edit this text!';;
}, false);

btnStart.addEventListener('click', function() {
  if (field.childNodes[0]) {
    observer.observe(field.childNodes[0], options);
    doLogAndBtn('Observing for mutations: STARTED');
}, false);

btnStop.addEventListener('click', function() {
  doLogAndBtn('STOPPED observing for mutations');
}, false);