Detect changes in the DOM

Question

I want to execute a function when some div or input are added to the html. Is this possible?

For example, a text input is added, then the function should be called.

Answer 1

Ultimate approach so far, with smallest code:

(IE11+, FF, Webkit)

Using MutationObserver and falling back to the deprecated Mutation events if needed:
(Example below if only for DOM changes concerning nodes appended or removed)

var observeDOM = (function(){
  var MutationObserver = window.MutationObserver || window.WebKitMutationObserver;

  return function( obj, callback ){
    if( !obj || obj.nodeType !== 1 ) return; 

    if( MutationObserver ){
      // define a new observer
      var mutationObserver = new MutationObserver(callback)

      // have the observer observe for changes in children
      mutationObserver.observe( obj, { childList:true, subtree:true })
      return mutationObserver
    }
    
    // browser support fallback
    else if( window.addEventListener ){
      obj.addEventListener('DOMNodeInserted', callback, false)
      obj.addEventListener('DOMNodeRemoved', callback, false)
    }
  }
})()


//------------< DEMO BELOW >----------------

// add item
var itemHTML = "<li><button>list item (click to delete)</button></li>",
    listElm = document.querySelector('ol');

document.querySelector('body > button').onclick = function(e){
  listElm.insertAdjacentHTML("beforeend", itemHTML);
}

// delete item
listElm.onclick = function(e){
  if( e.target.nodeName == "BUTTON" )
    e.target.parentNode.parentNode.removeChild(e.target.parentNode);
}
    
// Observe a specific DOM element:
observeDOM( listElm, function(m){ 
   var addedNodes = [], removedNodes = [];

   m.forEach(record => record.addedNodes.length & addedNodes.push(...record.addedNodes))
   
   m.forEach(record => record.removedNodes.length & removedNodes.push(...record.removedNodes))

  console.clear();
  console.log('Added:', addedNodes, 'Removed:', removedNodes);
});


// Insert 3 DOM nodes at once after 3 seconds
setTimeout(function(){
   listElm.removeChild(listElm.lastElementChild);
   listElm.insertAdjacentHTML("beforeend", Array(4).join(itemHTML));
}, 3000);

<button>Add Item</button>
<ol>
  <li><button>list item (click to delete)</button></li>
  <li><button>list item (click to delete)</button></li>
  <li><button>list item (click to delete)</button></li>
  <li><button>list item (click to delete)</button></li>
  <li><em>&hellip;More will be added after 3 seconds&hellip;</em></li>
</ol>

Answer 2

2015 update, new MutationObserver is supported by modern browsers:

Chrome 18+, Firefox 14+, IE 11+, Safari 6+

If you need to support older ones, you may try to fall back to other approaches like the ones mentioned in this 5 (!) year old answer below. There be dragons. Enjoy :)

---

Someone else is changing the document? Because if you have full control over the changes you just need to create your own domChanged API - with a function or custom event - and trigger/call it everywhere you modify things.

The DOM Level-2 has Mutation event types, but older version of IE don't support it. Note that the mutation events are deprecated in the DOM3 Events spec and have a performance penalty.

You can try to emulate mutation event with onpropertychange in IE (and fall back to the brute-force approach if non of them is available).

For a full domChange an interval could be an over-kill. Imagine that you need to store the current state of the whole document, and examine every element's every property to be the same.

Maybe if you're only interested in the elements and their order (as you mentioned in your question), a getElementsByTagName("*") can work. This will fire automatically if you add an element, remove an element, replace elements or change the structure of the document.

I wrote a proof of concept:

(function (window) {
    var last = +new Date();
    var delay = 100; // default delay

    // Manage event queue
    var stack = [];

    function callback() {
        var now = +new Date();
        if (now - last > delay) {
            for (var i = 0; i < stack.length; i++) {
                stack[i]();
            }
            last = now;
        }
    }

    // Public interface
    var onDomChange = function (fn, newdelay) {
        if (newdelay) delay = newdelay;
        stack.push(fn);
    };

    // Naive approach for compatibility
    function naive() {

        var last = document.getElementsByTagName('*');
        var lastlen = last.length;
        var timer = setTimeout(function check() {

            // get current state of the document
            var current = document.getElementsByTagName('*');
            var len = current.length;

            // if the length is different
            // it's fairly obvious
            if (len != lastlen) {
                // just make sure the loop finishes early
                last = [];
            }

            // go check every element in order
            for (var i = 0; i < len; i++) {
                if (current[i] !== last[i]) {
                    callback();
                    last = current;
                    lastlen = len;
                    break;
                }
            }

            // over, and over, and over again
            setTimeout(check, delay);

        }, delay);
    }

    //
    //  Check for mutation events support
    //

    var support = {};

    var el = document.documentElement;
    var remain = 3;

    // callback for the tests
    function decide() {
        if (support.DOMNodeInserted) {
            window.addEventListener("DOMContentLoaded", function () {
                if (support.DOMSubtreeModified) { // for FF 3+, Chrome
                    el.addEventListener('DOMSubtreeModified', callback, false);
                } else { // for FF 2, Safari, Opera 9.6+
                    el.addEventListener('DOMNodeInserted', callback, false);
                    el.addEventListener('DOMNodeRemoved', callback, false);
                }
            }, false);
        } else if (document.onpropertychange) { // for IE 5.5+
            document.onpropertychange = callback;
        } else { // fallback
            naive();
        }
    }

    // checks a particular event
    function test(event) {
        el.addEventListener(event, function fn() {
            support[event] = true;
            el.removeEventListener(event, fn, false);
            if (--remain === 0) decide();
        }, false);
    }

    // attach test events
    if (window.addEventListener) {
        test('DOMSubtreeModified');
        test('DOMNodeInserted');
        test('DOMNodeRemoved');
    } else {
        decide();
    }

    // do the dummy test
    var dummy = document.createElement("div");
    el.appendChild(dummy);
    el.removeChild(dummy);

    // expose
    window.onDomChange = onDomChange;
})(window);

Usage:

onDomChange(function(){ 
    alert("The Times They Are a-Changin'");
});

This works on IE 5.5+, FF 2+, Chrome, Safari 3+ and Opera 9.6+

Answer 3

The following example was adapted from Mozilla Hacks' blog post and is using MutationObserver.

// Select the node that will be observed for mutations
var targetNode = document.getElementById('some-id');

// Options for the observer (which mutations to observe)
var config = { attributes: true, childList: true };

// Callback function to execute when mutations are observed
var callback = function(mutationsList) {
    for(var mutation of mutationsList) {
        if (mutation.type == 'childList') {
            console.log('A child node has been added or removed.');
        }
        else if (mutation.type == 'attributes') {
            console.log('The ' + mutation.attributeName + ' attribute was modified.');
        }
    }
};

// Create an observer instance linked to the callback function
var observer = new MutationObserver(callback);

// Start observing the target node for configured mutations
observer.observe(targetNode, config);

// Later, you can stop observing
observer.disconnect();

Browser support: Chrome 18+, Firefox 14+, IE 11+, Safari 6+

Answer 4

I have recently written a plugin that does exactly that - jquery.initialize.
(NPM link - different NPM/GitHub user name, same author)

You use it the same way as .each function

$(".some-element").initialize( function(){
    $(this).css("color", "blue"); 
});

The difference from .each is - it takes your selector, in this case .some-element and wait for new elements with this selector in the future, if such element will be added, it will be initialized too.

In our case initialize function just change element color to blue. So if we'll add new element (no matter if with ajax or even F12 inspector or anything) like:

$("<div/>").addClass('some-element').appendTo("body"); //new element will have blue color!

Plugin will init it instantly. Also plugin makes sure one element is initialized only once. So if you add element, then .detach() it from body and then add it again, it will not be initialized again.

$("<div/>").addClass('some-element').appendTo("body").detach()
    .appendTo(".some-container");
//initialized only once

Plugin is based on MutationObserver - it will work on IE9 and 10 with dependencies as detailed on the readme page.

Answer 5

or you can simply Create your own event, that run everywhere

 $("body").on("domChanged", function () {
                //dom is changed 
            });


 $(".button").click(function () {

          //do some change
          $("button").append("<span>i am the new change</span>");

          //fire event
          $("body").trigger("domChanged");

        });

Full example http://jsfiddle.net/hbmaam/Mq7NX/

Answer 6

MutationObserver = window.MutationObserver || window.WebKitMutationObserver;

var observer = new MutationObserver(function(mutations, observer) {
    // fired when a mutation occurs
    console.log(mutations, observer);
    // ...
});

// define what element should be observed by the observer
// and what types of mutations trigger the callback
observer.observe(document, {
  subtree: true,
  attributes: true
  //...
});

Complete explanations: https://stackoverflow.com/a/11546242/6569224

Answer 7

Use the MutationObserver interface as shown in Gabriele Romanato's blog

Chrome 18+, Firefox 14+, IE 11+, Safari 6+

// The node to be monitored
var target = $( "#content" )[0];

// Create an observer instance
var observer = new MutationObserver(function( mutations ) {
  mutations.forEach(function( mutation ) {
    var newNodes = mutation.addedNodes; // DOM NodeList
    if( newNodes !== null ) { // If there are new nodes added
        var $nodes = $( newNodes ); // jQuery set
        $nodes.each(function() {
            var $node = $( this );
            if( $node.hasClass( "message" ) ) {
                // do something
            }
        });
    }
  });    
});

// Configuration of the observer:
var config = { 
    attributes: true, 
    childList: true, 
    characterData: true 
};

// Pass in the target node, as well as the observer options
observer.observe(target, config);

// Later, you can stop observing
observer.disconnect();

Answer 8

How about extending a jquery for this?

   (function () {
        var ev = new $.Event('remove'),
            orig = $.fn.remove;
        var evap = new $.Event('append'),
           origap = $.fn.append;
        $.fn.remove = function () {
            $(this).trigger(ev);
            return orig.apply(this, arguments);
        }
        $.fn.append = function () {
            $(this).trigger(evap);
            return origap.apply(this, arguments);
        }
    })();
    $(document).on('append', function (e) { /*write your logic here*/ });
    $(document).on('remove', function (e) { /*write your logic here*/ });

Jquery 1.9+ has built support for this(I have heard not tested).

Answer 9

8 years later, here is my solution using MutationObserver and RxJS

observeDOMChange(document.querySelector('#dom-changes-here'))
  .subscribe(val => log('DOM-change detected'));

The main difference from the other approaches is to fire a CustomEvent when DOM changes, and listen to the event debounced to execute user logic efficiently with the following features;

• Debounce consecutive DOM changes to prevent too many executions
• Stop watching after the given time
• Removes event listeners/subscribers after stop watching DOM changes
• Useful to watch DOM change happened in a framework, e.g., Angular

import { fromEvent, timer} from 'rxjs';
import { debounceTime, takeUntil, tap } from 'rxjs/operators';

function observeDOMChange(el, options={}) {
  options = Object.assign({debounce: 100, expires: 2000}, options);

  const observer = new MutationObserver(list =>  {
    el.dispatchEvent(new CustomEvent('dom-change', {detail: list}));
  });
  observer.observe(el, {attributes: false, childList: true, subtree: true });

  let pipeFn;
  if (options.expires) {
    setTimeout(_ => observer.disconnect(), options.expires);
    pipeFn = takeUntil(timer(options.expires));
  } else {
    pipeFn = tap(_ => _); 
  }

  return fromEvent(el, 'dom-change')
    .pipe(pipeFn, debounceTime(options.debounce));
}

Demo at stackblitz.

Answer 10

Found the question so updating with a solution in 2022.

We have seen different solutions which mostly involve MutationObserver.

If anyone wants to record the DOM changes and store them to replay after some time, they can use rrweb

Edit:

Adding example, here are the hints:

rrweb you can use via CDN or npm

Let's take the example of CDN for recording the DOM changes events:

Step 1: just include following script tag in the <HTML><head> tag

<script src="https://cdn.jsdelivr.net/npm/rrweb@2.0.0-alpha.2/dist/rrweb-all.js" crossorigin="anonymous"></script>

Step 2: and add the below code in your code to capture the events generated by rrweb.

<script>
var events = [];
rrweb.record({
    emit(event) {
       events.push(event);
       // you can store this event anywhere and you can replay them later. ex: some JSON file, or DB
    }
});

</script>

This example is mostly for recording events for any web application.

To know and understand in the detail (how to record/replay), please read from rrweb documentation.

Replayer Example:

This was for debugging, however adding here so that anyone can check replayed side as well:

Replayer Example

Answer 11

Use TrackChanges for detect html changes. Link: https://www.npmjs.com/package/track-changes-js

Example

 let button = document.querySelector('.button');

 trackChanges.addObserver('buttonObserver', () => button);
 
 trackChanges.addHandler('buttonObserver', buttonHandler);

 function buttonHandler(button) {
   console.log(`Button created: ${button}`);
 }