Geronimo served its purpose well, but these days I'd recommend Rellax.

Geronimo is a jQuery/Zepto plugin that makes parallax backgrounds super-simple. No annoying configuration, frustrating math, or general misery. Just install, call, and you're good-to-go!

First, include either jQuery or Zepto on the page, followed by Geronimo.

<script src="path/to/jquery.min.js"></script>
<script src="path/to/geronimo.min.js"></script>

Then call .geronimo() on the background elements you'd like to parallaxify.

<section class="section">
  <div class="section-background" style="background-image: url('some/background/image.jpg')"></div>
  <!-- the rest of your section content here -->
</section>

<script>
  $( document ).ready( function() {
    $( '.section-background' ).geronimo();
  } );
</script>

You can specify the speed of the effect as slow, medium (default), or fast like so:

<script>
  $( document ).ready( function() {
    $( '.section-background' ).geronimo( { speed: 'slow' } );
  } );
</script>

Geronimo is available on NPM and Bower.

npm install geronimo --save

bower install geronimo --save

IE10+, all recent versions of everything else.

Assuming you have Node.js and NPM installed...

$ npm install
$ gulp

If not, here's how you do that.

Geronimo is licensed under the MIT License.