Sticky footer after complete scroll - html

Question

I am trying to create a "see-also" button that is located on the bottom of the page.
When the user reaches the bottom and decides to scroll back up, I want it to stick to the bottom of the viewport.
I have been trying with position:sticky but then it is already sticked to the bottom of the viewport when the page just loaded. I only want this after a complete scroll down.
Any clues?
Thanks in advance.

Answer 1

This is an example with javascript (see result sticky button on scroll top
const DIRECTION_BOTTOM = 1;
const DIRECTION_TOP = 0;
let previousScroll = 0;
let direction = scrollY === 0 ? DIRECTION_BOTTOM : DIRECTION_TOP;
window.addEventListener('scroll', function(){
const scrollY = window.scrollY;
if(direction === DIRECTION_TOP && previousScroll < scrollY){
direction = DIRECTION_BOTTOM;
// remove sticky
document.getElementById("sticky").classList.remove("show");
}
else if(direction === DIRECTION_BOTTOM && previousScroll > scrollY ){
direction = DIRECTION_TOP;
// Add sticky
document.getElementById("sticky").classList.add("show");
}
previousScroll = scrollY;
})

Answer 2

You can create this functionality with JQuery by creating a function which calculates when an element is in the viewport. If the button enters the viewport, add a class which makes the element position: sticky. There are different ways to approach this problem but one solution is something like this:
$.fn.isInViewport = function() {
var elementTop = $(this).offset().top;
var elementBottom = elementTop + $(this).outerHeight();
var viewportTop = $(window).scrollTop();
var viewportBottom = viewportTop + $(window).height();
return elementBottom > viewportTop && elementTop < viewportBottom;
};
$(window).on("scroll", function() {
if($('#button').isInViewport()) {
$('#button').addClass('sticky');
}
});
body {
text-align: center;
}
.button {
padding: 6px 12px;
}
.div {
width: 100%;
height: 250px;
color: #fff;
}
.div1 {
background: blue;
}
.div2 {
background: red;
}
.div3 {
background: purple;
}
.sticky {
position: sticky;
position: -webkit-sticky;
position: -moz-sticky;
position: -ms-sticky;
position: -o-sticky;
height: 100%;
bottom: 5px;
}
<script src="https://code.jquery.com/jquery-3.4.1.min.js"></script>
<div class="div div1">Filler div 1</div>
<div class="div div2">Filler div 2</div>
<div class="div div3">Filler div 3</div>
<button type="button" class="button" id="button">See Also</button>

Answer 3

Scrambled everything together and this is working now:
window.onscroll = function(ev) {
if ((window.innerHeight + window.scrollY) >= document.body.scrollHeight) {
document.getElementById("see-also").classList.add("sticky");
}
};
Thanks you everyone