how-to-actually-do-mutation-observer.js

// Docs:
// https://developer.mozilla.org/en-US/docs/Web/API/MutationObserver#MutationObserverInit
//
// This is what it actually means:
// =========================================================================================================

var $elementToStretch = $('#the-element');

var debouncedStretchInnards = _.debounce(stretchInnards);
var $allAncestors = $elementToStretch.parents(); 
editorMD.ancestorObservers = _.reduce($allAncestors, function (memo, ancestorRawDOMElement) {
  var observer = new MutationObserver(function onMutation(){ debouncedStretchInnards(); });
  observer.observe(ancestorRawDOMElement, { attributes: true, attributeOldValue: true, attributeFilter: ['style'] }); 

  // Track ancestor observer.
  memo.push(observer);
  return memo;
}, []);

// Then in onRemove, call `.disconnect()` on each "observer" in `editorMD.ancestorObservers`.