casper/assets/js/sticky-nav-title.js

62 lines
1.6 KiB
JavaScript

/* eslint-env browser */
/**
* Nav/Title replacement
* Used on invividual post pages, displays the post title in place of the nav
* bar when scrolling past the title
*
* Usage:
* ```
* Casper.stickyTitle({
* navSelector: '.site-nav-main',
* titleSelector: '.post-full-title',
* activeClass: 'nav-post-title-active'
* });
* ```
*/
(function (window, document) {
// set up Casper as a global object
if (!window.Casper) {
window.Casper = {};
}
window.Casper.stickyNavTitle = function stickyNavTitle(options) {
var nav = document.querySelector(options.navSelector);
var title = document.querySelector(options.titleSelector);
var lastScrollY = window.scrollY;
var ticking = false;
function onScroll() {
lastScrollY = window.scrollY;
requestTick();
}
function requestTick() {
if (!ticking) {
requestAnimationFrame(update);
}
ticking = true;
}
function update() {
var trigger = title.getBoundingClientRect().top + window.scrollY;
var triggerOffset = title.offsetHeight + 35;
// show/hide post title
if (lastScrollY >= trigger + triggerOffset) {
nav.classList.add(options.activeClass);
} else {
nav.classList.remove(options.activeClass);
}
ticking = false;
}
window.addEventListener('scroll', onScroll, {passive: true});
update();
};
})(window, document);