mutation-watcher

MutationWatcher is a JavaScript library that comes to help make DOM mutation observing fast and easy.

MutationWatcher uses MutationObserver API (in new browsers) or old-fashioned (deprecated) way with Mutation events (in browsers that doesn't support newest API) as a way to react to changes in DOM. Actually it works in all browsers that support any of this APIs.

Install

bower:

$ bower install mutation-watcher

npm

$ npm install mutation-watcher

Usage

// Querying the target element
var target = document.querySelector('#signin-button');
 
// Options
var options = { attributes: [ 'pressed', 'focused', 'active'] };
 
// Creating the watcher instance
var watcher = new MutationWatcher(function(mutationData) { console.log(mutationData); });
 
// Finally starting the watcher
watcher.watch(target, options);
 
// Disconnecting from it
watcher.disconnect();

API

The MutationWatcher library exports a single object - class called MutationWatcher. The class allows to create a new instance of DOM mutation watcher.

Constructor

MutationWatcher()

Constructor for instantiating new DOM mutation watchers.

MutationWatcher(
    function callback,
    bool customEvents
);

Parameters

• callback. Optional. Defaults to null. The function which will be called per each DOM mutation. The watcher will call this function with two arguments. The first is a MutationData object. The second is the current instance of a MutationWatcher.
• customEvents. Optional. Defaults to false if callback provided and true if callback is null. If set to true then custom events will be triggered on specified target.

Note

If the class instance created without any argument, then customEvents will be set to true by default. If no callback provided or it's null then all MutationData objects will be added to the queue and available to return using takeRecords method.

Instance methods

• void watch( Object target, Object options );
• void disconnect();
• Array takeRecords();

watch()

Registers the MutationWatcher instance to receive notifications of DOM mutations on the specified node.

void watch(
    Object target,
    Object options
);

Parameters

• target. Optional. Defaults to window.document. The Node or a string representing the CSS selector for target node on which to observe DOM mutations.
• options. Optional. Defaults to all. An options object specifies which DOM mutations should be reported.

Note

If no target provided then the window.document will be used. If options object not provided then default options will be used.

disconnect()

Stops the MutationWatcher instance from receiving notifications of DOM mutations. Until the watch() method is used again, watcher's callback will not be invoked.

void disconnect();

takeRecords()

Empties the MutationWatcher instance's record queue and returns what was in there.

Array takeRecords();

Return value

Returns an Array of MutationData objects.

MutationWatcher Options

MutationWatcher options is an object which can specify the following properties:

• attributes - Set to true if mutations to target's attributes are to be observed.
• elements - Set to true if additions and removals of the target node's child elements (including text nodes) 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.
• matchAttributes - Set to an array of attribute local names (without namespace) if not all attribute mutations need to be observed.
• matchElements - Set to an array of CSS selectors or html elements if not all element mutations need to be observed.
• matchCharacterDataElements - Set to an array of CSS selectors or html elements if not all characterData mutations need to be observed.
• all - Shorthand. Set to true if attributes, elements and characterData need to be observed.

Default options

Options can be passed to watch() method as a plain string with single option or as an object with a combination of options.

// Single option can be passed as a string
var singleOption = 'attributes'; // or 'elements', 'characterData', 'all'
watcher1.watch(callback, singleOption);
 
// To combine options use object notation
var optionsObj = {
    elements: true,
    subtree: true,
    // Filter elements
    matchElements: ['img.photo', 'div.wall-post', actualNodeElement]
};
watcher2.watch(callback, optionsObj);
 
// or
optionsObj = {
    elements: ['img.photo', 'div.wall-post', actualNodeElement],
    subtree: true
};
watcher3.watch(callback, optionsObj); 

If watch() called without the options or it's null then default options will be used. The default options object looks following:

var watcher = new MutationWatcher(callback);
watcher.watch(target, null);
console.log(watcher._config);
/* prints out
{
    attributes: true,
    elements: true,
    characterData: true,
    attributeOldValue: true
    characterDataOldValue: true,
    subtree: false
}
*/

MutationData

MutationData 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 elements if it was a mutation to the tree of nodes.
target	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 elements, it is the node whose children changed.
addedNodes	NodeList	Return the nodes added. Will be a null if no nodes were added.
removedNodes	NodeList	Return the nodes removed. Will be a null if no nodes were removed.
previousSibling	Node	Return the previous sibling of the added or removed nodes, or null.
nextSibling	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 elements, it is null.
newValue	String	The return value dependents on the type. For attributes, it is the value of the changed attribute after the change. For characterData, it is the data of the changed node after the change. For elements, it is null.

Custom Events

It's possible to subscribe to custom mutation events instead of using callback passed to the constructor. Default event names can be changed using the static object called customEventsNames on MutationWatcher class.

To enable custom events on a specific target, it needs to set customEvents property to true and invoke watch() method with or without any arguments.

var watcher = new MutationWatcher(null,  true);
watcher.watch(myButton);
 
// Subscribing for attribute change
myButton.addEventListener(MutationWatcher.customEventsNames.attributes, function(event) {
    // Mutation data available in `details` property
    var mutationData = event.details;
}, false);

Supported browsers:

• Chrome
• Firefox
• IE9+
• Safari
• Opera

Running tests

Install dependencies:

$ npm install

Run them:

$ grunt test

Changelog

1.0.2 - September 7, 2015

• Moved from jshint to eslint
• Test improvements
• Updated npm dependencies
• Bug fixes

Author

Bohdan Shtepan

http://modern-dev.com

Please feel free to reach out to me if you have any questions or suggestions.

License

MIT