Is there a JavaScript / jQuery DOM change listener?

Question

Essentially I want to have a script execute when the contents of a DIV change. Since the scripts are separate (content script in the Chrome extension & webpage script), I need a way simply observe changes in DOM state. I could set up polling but that seems sloppy.

Answer 1

For a long time, DOM3 mutation events were the best available solution, but they have been deprecated for performance reasons. DOM4 Mutation Observers are the replacement for deprecated DOM3 mutation events. They are currently implemented in modern browsers as MutationObserver (or as the vendor-prefixed WebKitMutationObserver in old versions of Chrome):

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
  //...
});

This example listens for DOM changes on document and its entire subtree, and it will fire on changes to element attributes as well as structural changes. The draft spec has a full list of valid mutation listener properties:

childList

• Set to true if mutations to target's children 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 a list of attribute local names (without namespace) if not all attribute mutations need to be observed.

(This list is current as of April 2014; you may check the specification for any changes.)