I ran into this same issue recently, posted the my solution also here:
Preventing element from displaying on top of footer when using position:fixed
You can achieve a solution leveraging the position property of the element with jQuery, switching between the default value (static for divs), fixed and absolute.
You will also need a container element for your fixed element. Finally, in order to prevent the fixed element to go over the footer, this container element can't be the parent of the footer.
The javascript part involves calculating the distance in pixels between your fixed element and the top of the document, and comparing it with the current vertical position of the scrollbar relatively to the window object (i.e. the number of pixels above that are hidden from the visible area of the page) every time the user scrolls the page.
When, on scrolling down, the fixed element is about to disappear above, we change its position to fixed and stick on top of the page.
This causes the fixed element to go over the footer when we scroll to the bottom, especially if the browser window is small.
Therefore, we will calculate the distance in pixels of the footer from the top of the document and compare it with the height of the fixed element plus the vertical position of the scrollbar: when the fixed element is about to go over the footer, we will change its position to absolute and stick at the bottom, just over the footer.
Here's a generic example.
The HTML structure:
<div id="content">
<div id="leftcolumn">
<div class="fixed-element">
This is fixed
</div>
</div>
<div id="rightcolumn">Main content here</div>
<div id="footer"> The footer </div>
</div>
The CSS:
#leftcolumn {
position: relative;
}
.fixed-element {
width: 180px;
}
.fixed-element.fixed {
position: fixed;
top: 20px;
}
.fixed-element.bottom {
position: absolute;
bottom: 356px; /* Height of the footer element, plus some extra pixels if needed */
}
The JS:
// Position of fixed element from top of the document
var fixedElementOffset = $('.fixed-element').offset().top;
// Position of footer element from top of the document.
// You can add extra distance from the bottom if needed,
// must match with the bottom property in CSS
var footerOffset = $('#footer').offset().top - 36;
var fixedElementHeight = $('.fixed-element').height();
// Check every time the user scrolls
$(window).scroll(function (event) {
// Y position of the vertical scrollbar
var y = $(this).scrollTop();
if ( y >= fixedElementOffset && ( y + fixedElementHeight ) < footerOffset ) {
$('.fixed-element').addClass('fixed');
$('.fixed-element').removeClass('bottom');
}
else if ( y >= fixedElementOffset && ( y + fixedElementHeight ) >= footerOffset ) {
$('.fixed-element').removeClass('fixed');
$('.fixed-element').addClass('bottom');
}
else {
$('.fixed-element').removeClass('fixed bottom');
}
});
