Clearly define objectives, geometry, and conditions.
Problem Definition
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"use strict";
OB_ready(OB_doWhenReady);function OB_doWhenReady() {
// localize everything
var ooohBoi = window.ooohBoi || {};
// local scope variables
ooohBoi.prev_scroll_pos = window.scrollY || document.body.scrollTop;
ooohBoi.cur_scroll_pos;
ooohBoi.scroll_direction = 'init';
ooohBoi.prev_scroll_direction = 0;
ooohBoi.header = document.querySelector('#header_pop'); // header ID
ooohBoi.header_pos = {
top: ooohBoi.header.offsetTop,
left: ooohBoi.header.offsetLeft,
};
ooohBoi.header_height = OB_outerHeight(ooohBoi.header);
// show-hide header with ease/transition
ooohBoi.header.style.transition = 'all 0.3s ease-out';
// update header height on window resize
ooohBoi.updateHeaderHeight = function() {
ooohBoi.header_height = OB_outerHeight(ooohBoi.header);
}
// listen "scroll" event and decide what to do
ooohBoi.checkScroll = function() {
ooohBoi.cur_scroll_pos = window.scrollY || document.body.scrollTop;
if (ooohBoi.cur_scroll_pos > ooohBoi.prev_scroll_pos) ooohBoi.scroll_direction = 'down';
else if (ooohBoi.cur_scroll_pos ooohBoi.header_height) {
OB_addClass(ooohBoi.header, 'im-hidden'); // for styling
ooohBoi.header.style.top = -1 * ooohBoi.header_height + "px";
ooohBoi.prev_scroll_direction = scroll_direction;
} else if (scroll_direction === 'up') {
OB_removeClass(ooohBoi.header, 'im-hidden');
ooohBoi.header.style.top = ooohBoi.header_pos.top + "px";
ooohBoi.prev_scroll_direction = scroll_direction;
}
}
// listen "scroll" and "resize" window events
window.addEventListener('scroll', ooohBoi.checkScroll);
window.addEventListener('resize', ooohBoi.updateHeaderHeight);
}function OB_outerHeight(el) {
var height = el.offsetHeight;
var style = getComputedStyle(el);
height += parseInt(style.marginTop) + parseInt(style.marginBottom);
return height;
}function OB_addClass(el, className) {
if (el.classList) el.classList.add(className);
else {
var current = el.className,
found = false;
var all = current.split(' ');
for (var i = 0; i < all.length, !found; i++) found = all[i] === className;
if (!found) {
if (current === '') el.className = className;
else el.className += ' ' + className;
}
}
}function OB_removeClass(el, className) {
if (el.classList) el.classList.remove(className);
else el.className = el.className.replace(new RegExp('(^|\\b)' + className.split(' ').join('|') + '(\\b|$)', 'gi'), ' ');
}function OB_ready(fn) {
if (document.readyState != 'loading') fn();
else if (document.addEventListener) document.addEventListener('DOMContentLoaded', fn);
else {
document.attachEvent('onreadystatechange', function() {
if (document.readyState != 'loading') fn();
});
}
}
