The MutationObserverInit
dictionary's optional attributes
property is used to specify whether or not to watch for attribute value changes on the node or nodes being observed.
Syntax
var options = { attributes: true | false }
Value
A Boolean value indicating whether or not to report through the callback any changes to the values of attributes on the node or nodes being monitored. The default value is false
.
If true
, the callback specified when observe()
was used to start observing the node or subtree will be called any time one or more attributes have changed on observed nodes.
You can expand the capabilities of attribute mutation monitoring using other options:
attributeFilter
lets you specify specific attribute names to monitor instead of monitoring all attributes.attributeOldValue
lets you specify whether or not you want the previous value of changed attributes to be included in theMutationRecord
'soldValue
property.subtree
lets you specify whether to watch the target node and all of its descendants (true
), or just the target node (false
).
If you set either attributeFilter
or attributeOldValue
to true
, attributes
is automatically assumed to be true
, even if you don't expressly set it as such.
Example
In this example, a Mutation Observer is set up to watch for changes to the status
and username
attributes in any elements contained within a subtree that displays the names of users in a chat room. This lets the code, for example, reflect changes to users' nicknames, or to mark them as away from keyboard (AFK) or offline.
function callback(mutationList) { mutationList.forEach(function(mutation) { switch(mutation.type) { case "attributes": notifyUser("Attribute name " + mutation.attributeName + " changed to " + mutation.target[mutation.attributeName] + " (was " + mutation.oldValue + ")"); break; } }); } var targetNode = document.querySelector("#target"); var observer = new MutationObserver(callback); observer.observe(targetNode, { attributes: true, attributeOldValue: true });
The callback()
function—which will be passed into the observe()
method when starting the observer, looks at each item in the list of MutationRecord
objects. For any items representing an attribute change (which can be detected by the value of MutationRecord.type
being "attributes"
), a function called notifyUser()
is used to tell the user the name of the attribute that changed as well as the attribute's new value (mutation.target[mutation.attributeName]
) and its old value (mutation.oldValue
).
When observe()
is called, the specified options are attributes
and attributeOldValue
, which means that changes to attribute values will be reported, and each mutation record will include the oldValue
property specifying the attribute's previous value.
Specifications
Specification | Status | Comment |
---|---|---|
DOM The definition of 'MutationObserverInit.attributes' in that specification. |
Living Standard |
Browser compatibility
Desktop | Mobile | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
attributes | Chrome
Full support
26
| Edge Full support 12 | Firefox
Full support
14
| IE Full support 11 | Opera Full support 15 | Safari
Full support
7
| WebView Android ? | Chrome Android
Full support
26
| Firefox Android
Full support
14
| Opera Android Full support 14 | Safari iOS
Full support
7
| Samsung Internet Android
Full support
1.5
|
Legend
- Full support
- Full support
- Compatibility unknown
- Compatibility unknown
- See implementation notes.
- See implementation notes.
- Requires a vendor prefix or different name for use.
- Requires a vendor prefix or different name for use.