<div class="vh-container">
  <div class="vh-line">
  </div>
  <p class="vh-display">
    window.innerHeight = <span id="inner-height">0</span>px
  </p>
</div>

<div class="body-container">
  <div class="body-line">
  </div>
  <p class="body-display">
    document.body.offsetHeight = <span id="body-offset">0</span>px
  </p>
</div>

<div class="information">
  endOfPage = <span id="page-end"></span>
  <p class="small">(window.innerHeight + window.pageYOffset >= document.body.offsetHeight)</p>
  <p>window.pageYOffset = <span id="y-offset">0</span>px</p>
</div>

<footer>
  Pen by <a href="https://www.jemimaabu.com" target="_blank" rel="noopener">Jemima Abu</a> <span class="heart">&hearts;</span>
</footer>

@import url("https://fonts.googleapis.com/css2?family=Lato&display=swap");

body {
  margin: 0;
  height: 250vh;
  position: relative;
  font-family: "Lato", sans-serif;
  background: #f1f1f1;
}

.vh-container {
  position: relative;
  height: 100vh;
}

.vh-line,
.body-line {
  width: 2px;
  z-index: 2;
}

.vh-line {
  position: absolute;
  height: 97vh;
  top: 1.5vh;
  margin-left: 5px;
  background-color: blue;
}

.vh-line:before {
  position: absolute;
  content: "";
  top: -1.5vh;
  width: 0;
  height: 0;
  border-left: 5px solid transparent;
  border-right: 5px solid transparent;
  border-bottom: 15px solid black;
}

.vh-line:after {
  position: absolute;
  content: "";
  bottom: -1.5vh;
  width: 0;
  height: 0;
  border-left: 5px solid transparent;
  border-right: 5px solid transparent;
  border-top: 15px solid black;
}

.vh-line:before,
.vh-line:after {
  left: -4px;
}

.vh-display {
  position: absolute;
  height: max-content;
  margin: auto;
  transform: rotateZ(-90deg) translateX(-50%);
  top: 0;
  bottom: 0;
  left: 25px;
  transform-origin: left;
}

.body-container {
  position: relative;
}

.body-line {
  position: fixed;
  top: 1.5vh;
  height: 100vh;
  right: 0;
  margin-right: 5px;
  background-color: orange;
}

.body-line:before {
  position: fixed;
  content: "";
  top: 0;
  width: 0;
  height: 0;
  border-left: 5px solid transparent;
  border-right: 5px solid transparent;
  border-bottom: 15px solid black;
}

.body-line:after {
  position: fixed;
  content: "";
  bottom: 0;
  width: 0;
  height: 0;
  border-left: 5px solid transparent;
  border-right: 5px solid transparent;
  border-top: 15px solid black;
}

.body-line:before,
.body-line:after {
  right: 1px;
}

.body-display {
  position: fixed;
  height: max-content;
  width: 30vh;
  text-align: center;
  margin: auto;
  transform: rotateZ(-90deg);
  top: 0;
  bottom: 0;
  transform-origin: right;
  right: 35px;
  z-index: 2;
}

#inner-height {
  color: blue;
}

#body-offset {
  color: orange;
}

.information {
  position: fixed;
  left: 0;
  right: 0;
  bottom: 0;
  top: 0;
  width: 50%;
  max-width: 300px;
  height: fit-content;
  margin: auto;
  text-align: left;
  font-weight: bold;
  font-family: "Lato", sans-serif;
  transition: opacity 500ms;
}

.information .small {
  font-size: 0.75rem;
  margin: 0;
}

.scroll-container p {
  margin: 0;
  position: fixed;
  right: 0;
  font-size: 1.5rem;
}

.previous-scroll-container {
  top: var(--previous-count);
}

.current-scroll-container {
  top: var(--current-count);
}

footer {
  position: absolute;
  bottom: 0;
  width: 100%;
  padding: 1em;
  text-align: center;
  background-color: #ffdfb9;
}

footer a {
  color: inherit;
  text-decoration: none;
}

footer .heart {
  color: #dc143c;
}

const pageEnd = document.getElementById("page-end");
const innerHeight = document.getElementById("inner-height");
const yOffset = document.getElementById("y-offset");
const bodyOffset = document.getElementById("body-offset");

const handleScroll = () => {
  const endOfPage =
    window.innerHeight + window.pageYOffset >= document.body.offsetHeight;
  yOffset.innerHTML = window.pageYOffset;

  if (endOfPage) {
    pageEnd.innerHTML = "true";
    pageEnd.style.color = "green";
  } else {
    pageEnd.innerHTML = "false";
    pageEnd.style.color = "red";
  }
};

var throttleWait;

const throttle = (callback, time) => {
  if (throttleWait) return;
  throttleWait = true;

  setTimeout(() => {
    callback();
    throttleWait = false;
  }, time);
};

window.addEventListener("load", () => {
  innerHeight.innerHTML = window.innerHeight;
  bodyOffset.innerHTML = document.body.offsetHeight;
});
window.addEventListener("scroll", () => {
  throttle(handleScroll, 250);
});