A utility function, for Greasemonkey scripts, that detects and handles AJAXed content.

waitForKeyElements.js

/* --- waitForKeyElements():  A utility function, for Greasemonkey scripts,
    that detects and handles AJAXed content.

    Usage example:

        waitForKeyElements (
            "div.comments"
            , commentCallbackFunction
        );

        //--- Page-specific function to do what we want when the node is found.
        function commentCallbackFunction (jNode) {
            jNode.text ("This comment changed by waitForKeyElements().");
        }

    IMPORTANT: This function requires your script to have loaded jQuery.
*/
function waitForKeyElements(
  selectorTxt /* Required: The jQuery selector string that
                        specifies the desired element(s).
                    */,
  actionFunction /* Required: The code to run when elements are
                        found. It is passed a jNode to the matched
                        element.
                    */,
  bWaitOnce /* Optional: If false, will continue to scan for
                        new elements even after the first match is
                        found.
                    */,
  iframeSelector /* Optional: If set, identifies the iframe to
                        search.
                    */,
) {
  let targetNodes, btargetsFound;

  if (typeof iframeSelector === 'undefined') {
    targetNodes = $(selectorTxt);
  } else {
    targetNodes = $(iframeSelector).contents().find(selectorTxt);
  }

  if (targetNodes && targetNodes.length > 0) {
    btargetsFound = true;
    /* --- Found target node(s).  Go through each and act if they
            are new.
        */
    targetNodes.each(function () {
      let jThis = $(this);
      let alreadyFound = jThis.data('alreadyFound') || false;

      if (!alreadyFound) {
        // --- Call the payload function.
        let cancelFound = actionFunction(jThis);
        if (cancelFound) {
          btargetsFound = false;
        } else {
          jThis.data('alreadyFound', true);
        }
      }
    });
  } else {
    btargetsFound = false;
  }

  // --- Get the timer-control variable for this selector.
  let controlObj = waitForKeyElements.controlObj || {};
  let controlKey = selectorTxt.replace(/[^\w]/g, '_');
  let timeControl = controlObj[controlKey];

  // --- Now set or clear the timer as appropriate.
  if (btargetsFound && bWaitOnce && timeControl) {
    // --- The only condition where we need to clear the timer.
    clearInterval(timeControl);
    delete controlObj[controlKey];
  } else {
    // --- Set a timer, if needed.
    if (!timeControl) {
      timeControl = setInterval(function () {
        waitForKeyElements(selectorTxt, actionFunction, bWaitOnce, iframeSelector);
      }, 300);
      controlObj[controlKey] = timeControl;
    }
  }
  waitForKeyElements.controlObj = controlObj;
}