How to find true bottom of a div?

Question

codepen You need to resize the codepen so the scroll shows up. I'm talking about the inner scroll inside of Content.

I want to know if the scroll is at the bottom of a div. I've seen this done for the page. When I scroll to the bottom of the div scrollTop shows 95 while scrollHeight gives me 210. How do I find true bottom?

var scroller = $('.fill-area-content');

var getHeight = function() {
  //console.log(scroller.scrollTop());
  console.log('IsAtBottom: ', isAtBottom(scroller));
}

var isAtBottom = function(scroller) {
  var atBottom = false;
  var asRawDom = scroller.get(0);

  console.log('scroll height', asRawDom.scrollHeight);
  console.log(asRawDom.scrollTop);
  //scrollHeight is 210 while Bottom is 95
  //How do I determine true bottom?

  return atBottom;
}

//Stuff I've messed with
/*
console.log(scroller.height());
  console.log($(document).height());
  console.log($(window).height());
  var testHeight = $(document).height() -      $(window).height();
  console.log(testHeight);
*/

<input type="button" onclick="getHeight()" value="Get Height"/>
<div class="flexbox-container">
    <div class="flexbox-item header">
        Header
    </div>

    <div class="flexbox-item flexbox-inner-container flexbox-item-grow">
        <div class="flexbox-item-grow fill-area-content">
          Content
            <br /><br />
            Emulates height 100% with a horizontal flexbox with stretch
            <br /><br />      
            This box with a border should fill the blue area except for the padding (just to show the middle flexbox item).  Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.
        </div>
    </div>

    <div class="flexbox-item footer">
        Footer
    </div>
</div>

.flexbox-container
{
    //width: 100%;
    height: 100%;

    display: flex;
    flex-direction: column;

    justify-content: flex-start; /* align items in Main Axis */
    align-items: stretch; /* align items in Cross Axis */
    align-content: stretch; /* Extra space in Cross Axis */

    background: rgba(255, 255, 255, .1);
}

.flexbox-inner-container
{
    display: flex;
    flex-direction: row;

    justify-content: flex-start; /* flex-start is the default.  align items in Main Axis */
    align-items: stretch; /* stretch is default.  align items in Cross Axis */
    align-content: stretch; /* stretch is default. Extra space in Cross Axis */
}

.flexbox-item-grow
{
    flex: 1; /* same as flex: 1 1 auto; */
}

.fill-area-content
{
    overflow: auto; 
}

//Fluff below here
*, *:before, *:after
{
    -moz-box-sizing: border-box;
    -webkit-box-sizing: border-box;
    box-sizing: border-box;
}


html, body
{
    width: 100%;
    height: 100%;

    margin: 0;
    padding: 0;
}

.flexbox-item
{
    padding: 8px;
}

.flexbox-item.header
{
    background: rgba(255, 0, 0, .1);
}
.flexbox-item.footer
{
    background: rgba(0, 255, 0, .1);
}
.flexbox-item.
{
    background: rgba(0, 0, 255, .1);
}


body
{
    background: #444444;

    color: #cccccc;
    font-size: 14px;

    font-family: Frutiger, "Frutiger Linotype", Univers, Calibri, "Gill Sans", "Gill Sans MT", "Myriad Pro", Myriad, "DejaVu Sans Condensed", "Liberation Sans", "Nimbus Sans L", Tahoma, Geneva, "Helvetica Neue", Helvetica, Arial, sans-serif;

}

Answer 1

The maximum value of scrollTop (and thus what you need to calculate to determine whether the scroll has moved to the bottom of the element) will be scrollHeight minus the height of the element - given what you describe I would assume the element is 115px tall. Here's a working example:

$('#foo').scroll(function() {
  var maxScrollTop = $(this).prop('scrollHeight') - $(this).height();
  if ($(this).scrollTop() == maxScrollTop) {
    console.log('scrolled to bottom!');
  }
});

#foo {
  height: 100px;
  overflow: scroll;
}
#content {
  height: 1000px;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="foo">
  <div id="content">Scroll down!</div>
</div>