weflock/assets/js/floating-header.js

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/* eslint-env browser */
/**
* Floating header
* Used on invividual post pages, displays a sticky header with progress indicator
*
* This JS is automatically applied for any template where you use the
* {{> floating-header}} partial
*/
(function (window, document) {
// set up Casper as a global object
if (!window.Casper) {
window.Casper = {};
}
window.Casper.floatingHeader = function floatingHeader() {
// NOTE: Scroll performance is poor in Safari
// - this appears to be due to the events firing much more slowly in Safari.
// Dropping the scroll event and using only a raf loop results in smoother
// scrolling but continuous processing even when not scrolling
var progressBar = document.querySelector('#reading-progress');
var header = document.querySelector('.floating-header');
var title = document.querySelector('.post-full-title');
var lastScrollY = window.scrollY;
var lastWindowHeight = window.innerHeight;
var lastDocumentHeight = document.body.clientHeight;
var ticking = false;
function onScroll() {
lastScrollY = window.scrollY;
requestTick();
}
function onResize() {
lastWindowHeight = window.innerHeight;
lastDocumentHeight = document.body.clientHeight;
requestTick();
}
function requestTick() {
if (!ticking) {
requestAnimationFrame(update);
}
ticking = true;
}
function update() {
var trigger = title.getBoundingClientRect().top + window.scrollY;
var triggerOffset = title.offsetHeight + 35;
var progressMax = lastDocumentHeight - lastWindowHeight;
// show/hide floating header
if (lastScrollY >= trigger + triggerOffset) {
header.classList.add('floating-active');
} else {
header.classList.remove('floating-active');
}
progressBar.setAttribute('max', progressMax);
progressBar.setAttribute('value', lastScrollY);
ticking = false;
}
window.addEventListener('scroll', onScroll, {passive: true});
window.addEventListener('resize', onResize, false);
update();
};
})(window, document);