Mutation observer example listening to changes in [disabled] and [hidden] attributes

observer.js

!function() {
  var emitter = {
    emit: console.dir.bind(console)
  }

  var disabled = 'disabled'
  var enabled = 'enabled'
  var hidden = 'hidden'
  var unhidden = 'unhidden'

  function emit(mutation) {
    var property = mutation.attributeName
    var target = mutation.target

    if (property === disabled) {
      emitter.emit(target[disabled] ? disabled : enabled, target)
    } else if (property === hidden) {
      emitter.emit(target[hidden] ? hidden : unhidden, target)
    }
  }

  var observer = new MutationObserver(function(mutations) {
    mutations.forEach(emit)
  });

  observer.observe(document.body, {
    subtree: true,
    attributes: true
  });
}();