Find out which element is scrolling

bookmarklet.js

javascript:!function() { var slice = Array.prototype.slice; function throttle(type, name, obj) { obj = obj || window; var running = false; var func = function() { if (running) { return; } running = true; requestAnimationFrame(function() { obj.dispatchEvent(new CustomEvent(name)); running = false; }); }; obj.addEventListener(type, func); } slice .call(document.querySelectorAll("*")) .filter( e => e.scrollWidth > e.offsetWidth || e.scrollHeight > e.offsetHeight ) .filter(e => { var style = window.getComputedStyle(e); return [style.overflow, style.overflowX, style.overflowY].some( e => e === "auto" || e === "scroll" ); }) .forEach(e => { var color = Math.floor(Math.random() * 16777215).toString(16); e.style.backgroundColor = "#" + color; throttle("scroll", "optimizedScroll", e); e.addEventListener("scroll", event => { console.log("%c[scroll]", "color: white; background-color:#" + color, event.target); }); }); }()

who-scrolls.js

(function() {
  var slice = Array.prototype.slice;

  function throttle(type, name, obj) {
    obj = obj || window;
    var running = false;
    var func = function() {
      if (running) {
        return;
      }
      running = true;
      requestAnimationFrame(function() {
        obj.dispatchEvent(new CustomEvent(name));
        running = false;
      });
    };
    obj.addEventListener(type, func);
  }

  slice
    .call(document.querySelectorAll("*"))
    .filter(
      e => e.scrollWidth > e.offsetWidth || e.scrollHeight > e.offsetHeight
    )
    .filter(e => {
      var style = window.getComputedStyle(e);
      return [style.overflow, style.overflowX, style.overflowY].some(
        e => e === "auto" || e === "scroll"
      );
    })
    .forEach(e => {
      var color = Math.floor(Math.random() * 16777215).toString(16);
      e.style.backgroundColor = "#" + color;
      throttle("scroll", "optimizedScroll", e);

      e.addEventListener("scroll", event => {
        console.log("%c[scroll]", "color: white; background-color:#" + color, event.target);
      });
    });
})();

This snippet will apply a random background-color to any scrolling element on the page, and log the color-coded element to the console on scroll events