A simple JavaScript function to catch when elements are added to a specified container element.

ondominsertfunction.js

/**
* A simple function to catch when elements are added to a specified container element. 
* @author Most of this code is from a StackOverflow post I can't find right now. I wrapped it into a reusable function.
* @param {HTMLElement} containerElement - The container element to watch for added nodes.
* @param {function} eventHandlerFunction - The function to call when a node is added to the containerElement.
*/
function onDOMInsert(containerElement, eventHandlerFunction) {
  if (typeof MutationObserver === 'function') {
    var observer = new MutationObserver(function (m) {
        for (var i = 0; i < m.length; i++) {
            if (m[i].addedNodes.length) {
                eventHandlerFunction();
                break;
            }
        }
    });
    observer.observe(containerElement, {childList: true});
  } else if (containerElement.addEventListener) {
    containerElement.addEventListener('DOMNodeInserted', eventHandlerFunction);
  } else {
    containerElement.attachEvent('onDOMNodeInserted', eventHandlerFunction);
  }
}