fullPage.js, as its author states, is a jQuery plugin which allows you to “create full screen pages fast and simple”.

How about using it to make a split-screen parallax fast and simple ?

First the required HTML structure:

<div id="splitscreen">
  <div class="section">
    <div class="column column-left">Left Side</div>
    <div class="column column-right">Right Side</div>
  </div>
</div>

Then init the fullPage.js, and customize the settings to your taste.

$(document).ready(function() {
  $('#splitscreen').fullpage({
    navigation: false,
    scrollingSpeed: 1000,
  });
});

Now the CSS for the split-screen:

#splitscreen > .section .column-left {
  float: left;
  width: 50%;
  color: #000;
  background: #fff;
}

#splitscreen > .section .column-right {
  float: right;
  width: 50%;
  color: #fff;
  background: #000;
}

#splitscreen > .section .column-left {
  transition: all 1s ease 0s;
  transform: translateY(100%);
  backface-visibility: hidden;
}

#splitscreen > .section .column-right {
  transition: all 1s ease 0s;
  transform: translateY(-100%);
  backface-visibility: hidden;
}

#splitscreen > .section.active {
  z-index: 1;
}

#splitscreen > .section.active .column-left {
  transform: translateY(0);
}

#splitscreen > .section.active .column-right {
  transform: translateY(0);
}

#splitscreen > .section.active~.section .column-left {
  transform: translateY(-100%);
}

#splitscreen > .section.active~.section .column-right {
  transform: translateY(100%);
}

/* prevent fullpage from "scrolling" the page */
#splitscreen {
  transform: translate3d(0px, 0px, 0px) !important;
}

#splitscreen > .section {
  position: absolute;
  top: 0;
  left: 0;
}

Split screen parallax demo.