{{APIRef("DOM")}}
MutationObserver provides developers a way to react to changes in a DOM. It is designed as a replacement for Mutation Events defined in the DOM3 Events specification.
Constructor
MutationObserver()
Constructor for instantiating new DOM mutation observers.
new MutationObserver( function callback );
Parameters
callback- The function which will be called on each DOM mutation. The observer will call this function with two arguments. The first is an array of objects, each of type
MutationRecord. The second is thisMutationObserverinstance.
Instance methods
void observe( {{domxref("Node")}} target, MutationObserverInit options ); |
void disconnect(); |
Array takeRecords(); |
Note: {{domxref("Node")}} target should not be confused with {{domxref("NodeJS")}}.
observe()
Registers the MutationObserver instance to receive notifications of DOM mutations on the specified node.
void observe(
{{domxref("Node")}} target,
MutationObserverInit options
);
Parameters
target- The {{domxref("Node")}} on which to observe DOM mutations.
options- A
MutationObserverInitobject, specifies which DOM mutations should be reported.
NOTE: Adding an observer to an element is just like addEventListener, if you observe the element multiple times it does not make a difference. Meaning if you observe element twice, the observe callback does not fire twice, nor will you have to run disconnect() twice. In other words, once an element is observed, observing it again with the same observer instance will do nothing. However if the callback object is different it will of course add another observer to it.
disconnect()
Stops the MutationObserver instance from receiving notifications of DOM mutations. Until the observe() method is used again, observer's callback will not be invoked.
void disconnect();
takeRecords()
Empties the MutationObserver instance's record queue and returns what was in there.
Array takeRecords();
Return value
Returns an Array of MutationRecords.
MutationObserverInit
MutationObserverInit is an object which can specify the following properties:
NOTE: At the very least,
childList, attributes, or characterData must be set to true. Otherwise, "An invalid or illegal string was specified" error is thrown.| Property | Description |
childList |
Set to true if additions and removals of the target node's child elements (including text nodes) are to be observed. |
attributes |
Set to true if mutations to target's attributes are to be observed. |
characterData |
Set to true if mutations to target's data are to be observed. |
subtree |
Set to true if mutations to not just target, but also target's descendants are to be observed. |
attributeOldValue |
Set to true if attributes is set to true and target's attribute value before the mutation needs to be recorded. |
characterDataOldValue |
Set to true if characterData is set to true and target's data before the mutation needs to be recorded. |
attributeFilter |
Set to an array of attribute local names (without namespace) if not all attribute mutations need to be observed. |
MutationRecord
MutationRecord is the object that will be passed to the observer's callback. It has the following properties:
| Property | Type | Description |
type |
String |
Returns attributes if the mutation was an attribute mutation, characterData if it was a mutation to a CharacterData node, and childList if it was a mutation to the tree of nodes. |
target |
{{domxref("Node")}} |
Returns the node the mutation affected, depending on the type. For attributes, it is the element whose attribute changed. For characterData, it is the CharacterData node. For childList, it is the node whose children changed. |
addedNodes |
{{domxref("NodeList")}} |
Return the nodes added. Will be an empty NodeList if no nodes were added. |
removedNodes |
{{domxref("NodeList")}} |
Return the nodes removed. Will be an empty NodeList if no nodes were removed. |
previousSibling |
{{domxref("Node")}} |
Return the previous sibling of the added or removed nodes, or null. |
nextSibling |
{{domxref("Node")}} |
Return the next sibling of the added or removed nodes, or null. |
attributeName |
String |
Returns the local name of the changed attribute, or null. |
attributeNamespace |
String |
Returns the namespace of the changed attribute, or null. |
oldValue |
String |
The return value depends on the type. For attributes, it is the value of the changed attribute before the change. For characterData, it is the data of the changed node before the change. For childList, it is null. |
Example usage
The following example was taken from this blog post.
// select the target node
var target = document.querySelector('#some-id');
// create an observer instance
var observer = new MutationObserver(function(mutations) {
mutations.forEach(function(mutation) {
console.log(mutation.type);
});
});
// 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();
Additional reading
- A brief overview
- A more in-depth discussion
- A screencast by Chromium developer Rafael Weinstein
- The mutation summary library
- The DOM standard which defines the
MutationObserverinterface
Browser compatibility
{{CompatibilityTable}}
| Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
|---|---|---|---|---|---|
| Basic support | 18 {{property_prefix("-webkit")}} 26 |
{{CompatGeckoDesktop(14)}} | 11 | 15 | 6.0 {{property_prefix("-webkit")}} |
| Feature | Android | Chrome for Android | Firefox Mobile (Gecko) | IE Phone | Opera Mobile | Safari Mobile |
|---|---|---|---|---|---|---|
| Basic support | {{CompatUnknown}} | 18 {{property_prefix("-webkit")}} 26 |
{{CompatGeckoMobile(14)}} | 11 (8.1) | 15 | 6 {{property_prefix("-webkit")}} 7 |