petr.js

function random(min, max) {
  return Math.floor(min + Math.random() * (max - min + 1));
}

function setStyle(element, style) {
  for (var s in style) {
    element.style[s] = style[s];
  }
}

function removeElement(el) {
  el.parentNode.removeChild(el);
}

const shakeSpeed = 40;
const shakePositionInterval = 250;
const appVersion = navigator.appVersion;

var cursor = null,
  posInterval = null,
  cursorPosX = 0,
  cursorPosY = 0,
  viewportPosX = 0,
  viewportPosY = 0,
  offsetX = 0,
  offsetY = 0,
  css = null,
  clickedElement = null;

function mousemoveHandler(e) {
  // Save the position of the fake cursor
  cursorPosX = e.pageX + offsetX;
  cursorPosY = e.pageY + offsetY;

  // Save the viewport position of the fake cursor (position without scroll)
  // We use this later to get the clicked element
  viewportPosX = e.clientX + offsetX;
  viewportPosY = e.clientY + offsetY;

  setStyle(cursor, { left: cursorPosX + "px", top: cursorPosY + "px" });
}

function elementClickHandler(e) {
  if (e.target === clickedElement) {
    // Actual mouse clicked element is the same as the element that the fake cursor would click.
    // This is because we triggered the click or that the positions of the mouse and the fake cursor are both over the same element.
    // Do nothing and pass on the click. Reset the clicked element.
    clickedElement = null;
  } else {
    // Actual mouse clicked element is NOT the same as the element that the fake cursor would click.
    // Get the element that the fake cursor would click and trigger click on that element.
    e.preventDefault();

    clickedElement = document.elementFromPoint(viewportPosX, viewportPosY);

    if (clickedElement) {
      clickedElement.click();
    }
  }
}

function setOffset() {
  offsetX = random(-shakeSpeed, shakeSpeed);
  offsetY = random(-shakeSpeed, shakeSpeed);
}

function start() {
  const cursorType = appVersion.includes("Windows") ? "windows" : "mac";
  
  cursor = document.createElement("div");

  cursor.setAttribute("id", "wds-parkinsonsCursor");
  cursor.setAttribute("class", cursorType);

  document.body.appendChild(cursor);
  
  document.addEventListener("mousemove", mousemoveHandler);

  document.addEventListener("click", elementClickHandler);

  posInterval = setInterval(setOffset, shakePositionInterval);

}

function stop() {

  if(cursor) {
    removeElement(cursor);
  }

  if(posInterval) {
    clearInterval(posInterval);
  }

  // TODO: remove listeners

}