MutationObserverInit.subtree

The MutationObserverInit dictionary's optional subtree property can be set to true to monitor the targeted node and all of its descendants. The default value, false, indicates only the target node itself is to be monitored for changes.

subtree can be used in concert with the other options to extend monitoring of attributes, text content, and child lists to the entire subtree rooted at the target node.

A Boolean value. The default, false, indicates that only the target node specified when calling MutationObserver.observe() is to be monitored for changes. Changing this value to true causes the entire subtree rooted at the specified target node to be monitored for the changes indicated by the other options.

For example, to watch the target node only for attribute changes, the MutationObserverInit passed into MutationObserver() can be:

var options = {
  attributes: true,
  subtree: false
};

Since the default value of subtree is false, line 3 is optional.

To monitor the entire subtree for attribute changes, set subtree to true:

var options = {
  attributes: true,
  subtree: true
};