nodeObserver - utility function for MutationObserver

gistfile1.js

/* example
nodeObserver(function log(info) {
  console.log(info);
  info.options.observer.disconnect();
}, {
  target: document,
  childList: true,
  subtree: true,
  addOnly: true
});

document.body.appendChild(document.createElement('div'));
document.body.insertAdjacentHTML('BeforeEnd', '<div></div><div></div>');
document.body.removeChild(document.body.lastElementChild);
setTimeout(function () {
  document.body.appendChild(document.createElement('div'));
}, 1000);
// -> log 3 info, not 5 info.
*/

/**
 * utility function for MutationObserver
 * @version 3.0.0
 * @link https://dom.spec.whatwg.org/#mutation-observers
 * @param {Function} callback
 * @param {Object} options
 * @returns {Object} options
 */
function nodeObserver(callback, options) {
  let hasOnly = options.addOnly || options.removeOnly;
  let nodesType = options.addOnly ? 'addedNodes' : 'removedNodes';

  let observer = new MutationObserver(mutations => {
    for (let record of mutations) {
      let nodes = record.type === 'childList' && hasOnly ?
        record[nodesType] :
        [null];

      for (let node of nodes) {
        callback({node, record, options});
      }
    }
  });

  observer.observe(options.target, options);

  return Object.assign(options, {observer, callback});
}