self contained classic BBS style page loading animation

386.js

// modified bbs loading animation from bootstrap 386
// https://github.com/kristopolous/BOOTSTRA.386
// view it in action at https://0w.nz

document.addEventListener("DOMContentLoaded", function () {
  $ = function $(selector, context = document) {
    return Array.from(context.querySelectorAll(selector));
  };
  _ = function _(action, obj, parent = document.body) {
    action == "add" ? parent.appendChild(obj) : parent.removeChild(obj);
  };
  (function () {
    var onePass = true;
      (character = { height: 20, width: 12.4 }),
      (pass = 0),
      (speedFactor = (1 / (1.25 || 1)) * 165000),
      (wrap = document.createElement("div")),
      (bar = wrap.appendChild(document.createElement("div"))),
      (cursor = document.createElement("div")),
      (height = window.innerHeight),
      (width = window.innerWidth),
      (rounds = (height * width) / speedFactor),
      (col = width),
      (row = height - character.height);

    wrap.id = "splash";
    bar.id = "bbs";
    cursor.id = "cursor";

    if (pass === 0) {
      _("add", wrap);
    } else {
      _("add", cursor);
      rounds /= 2;
      character.height *= 4;
    }
    cursor.innerHTML = bar.innerHTML = "▄";

    var l = setInterval(function () {
      for (var m = 0; m < rounds; m++) {
        col -= character.width;

        if (col <= 0) {
          col = width;
          row -= character.height;
        }
        if (row <= 0) {
          pass++;
          row = height - character.height;

          if (pass == 2) {
            _("rm", cursor);
            clearInterval(l);
          } else {
            _("rm", wrap, wrap.parentNode);
            if (onePass) {
              clearInterval(l);
            } else {
              _("add", cursor);
              rounds /= 2;
              character.height *= 4;
            }
          }
        }
        if (pass === 0) {
          bar.style.width = col + "px";
          wrap.style.height = row + "px";
        } else {
          cursor.style.right = col + "px";
          cursor.style.bottom = row + "px";
        }
      }
    }, 1);
  })();
});