How to fix div on scroll [closed]

If you scroll down the page in the following URL, the 'share' div will lock onto the browser:

http://knowyourmeme.com/memes/pizza-is-a-vegetable

I'm assuming they are applying a position: fixed; attribute. How can this be achieved with jQuery?

You can find an example below. Basically you attach a function to window's scroll event and trace scrollTop property and if it's higher than desired threshold you apply position: fixed and some other css properties.

jQuery(function($) {
  $(window).scroll(function fix_element() {
    $('#target').css(
      $(window).scrollTop() > 100
        ? { 'position': 'fixed', 'top': '10px' }
        : { 'position': 'relative', 'top': 'auto' }
    );
    return fix_element;
  }());
});

body {
  height: 2000px;
  padding-top: 100px;
}
code {
  padding: 5px;
  background: #efefef;
}
#target {
  color: #c00;
  font: 15px arial;
  padding: 10px;
  margin: 10px;
  border: 1px solid #c00;
  width: 200px;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div id="target">This <code>div</code> is going to be fixed</div>

On jQuery for designers there's a well written post about this, this is the jQuery snippet that does the magic. just replace #comment with the selector of the div that you want to float.

Note: To see the whole article go here: http://jqueryfordesigners.com/fixed-floating-elements/

$(document).ready(function () {
  var $obj = $('#comment');
  var top = $obj.offset().top - parseFloat($obj.css('marginTop').replace(/auto/, 0));

  $(window).scroll(function (event) {
    // what the y position of the scroll is
    var y = $(this).scrollTop();

    // whether that's below the form
    if (y >= top) {
      // if so, ad the fixed class
      $obj.addClass('fixed');
    } else {
      // otherwise remove it
      $obj.removeClass('fixed');
    }
  });
});

I made a mix of the answers here, took the code of @Julian and ideas from the others, seems clearer to me, this is what's left:

fiddle http://jsfiddle.net/wq2Ej/

jquery

//store the element
var $cache = $('.my-sticky-element');

//store the initial position of the element
var vTop = $cache.offset().top - parseFloat($cache.css('marginTop').replace(/auto/, 0));
  $(window).scroll(function (event) {
    // what the y position of the scroll is
    var y = $(this).scrollTop();

    // whether that's below the form
    if (y >= vTop) {
      // if so, ad the fixed class
      $cache.addClass('stuck');
    } else {
      // otherwise remove it
      $cache.removeClass('stuck');
    }
  });

css:

.my-sticky-element.stuck {
    position:fixed;
    top:0;
    box-shadow:0 2px 4px rgba(0, 0, 0, .3);
}