Parallax header

Simple parallax background image on a header

A work in progress. I'm still not happy with this, but getting there

Using a little CSS and a small snippet of vanilla JavaScript to emulate the header background used on LinkedIn.

This is a demo of a parallax header image, below a navigation block, followed by a local navigation block and content. As used on the Tesco 2016 Mother's Day page.

Core method is an extension of Sticky header. Using CSS transforms and a little script. Not too sure about the debounce method used, will see how it performs.

Mark up

<header id=hero class=hero>
  <div id=hero_bg class="hero-bg img-bg" data-src="digital-tunnel.jpg"><div></div></div>
  <div id=hero_copy class=hero-copy>
    <h1>Heading</h1>
    <p>Copy</p>
  </div>
</header>

CSS

The image is set as a background on .hero-bg and placed via position : absolute so even without JavaScript support the image displays. Once the script kicks in it adds the class .hero_fixed to change to position : fixed

WIP - See demo source…

JavaScript

Requires detect CSS transform3d browser support.

Three id's and two class names are hard coded, but may be easily externalised.

var ParallaxHeader = (function () {
  "use strict";
  var hero = document.getElementById("hero"),
      hero_bg = document.getElementById("hero_bg"),
      hero_copy = document.getElementById("hero_copy"),
      lastScrollTop = -1;

The _redrawLoop function loops continuously, without the more usual setTimeout or setInterval. By using requestAnimationFrame instead much faster, and smoother, animations are possible.

Note: obj.style is more performant than obj.setAttribute("style", ...).

  var _redrawLoop = function () {
    WIP - See demo source…
  };

The _setVars function is called on initialisation and when the window is resized. It adjusts the height of the background image to suit header dimensions.

A little extra height is required to ensure there's no body background bleed-through when scrolling extremely quickly. With the figures used allow the background to overscan the header by approximately 23%. Set to 10% above and 13% below.

Note: offsetHeight is more performant than getBoundingClientRect().

  var _setVars = function () {
    WIP - See demo source…
  };

A check to ensure transform3d support before initialisation. Please note the resize event listener would be better served debounced when used in full production, a little beyond scope here.

  WIP - See demo source…
}());

Google compiled parallax header

WIP - See demo source…