DragStart.js

function touchStart(startX, startY) {
  var menuOpen = document.querySelector(".menu.menu--visible");

  if (menuOpen !== null) {
    isOpen = true;
  } else {
    isOpen = false;
  }

  menu.classList.add("no-transition");
  appMenu.classList.add("no-transition");

  isMoving = true;
  menuWidth = document.querySelector(".app-menu").offsetWidth;
  lastX = startX;
  lastY = startY;

  if (isOpen) {
    moveX = 0;
  } else {
    moveX = -menuWidth;
  }

  dragDirection = "";
  menu.classList.add("menu--background-visible"); 
  // why is this being added? ‘.menu--background-visible .menu-background’ makes the overlay 
  // ‘active’, displaying it on the DOM for those sweet opacity changes.
}