(function() {
'use strict';
var THRESHOLD = 300; // px (show after meaningful scroll)
var BUTTON_ID = 'back-to-top';
function throttle(fn, limit) {
var inThrottle, lastFunc, lastTime;
return function() {
var context = this, args = arguments;
if (!inThrottle) {
fn.apply(context, args);
lastTime = Date.now();
inThrottle = true;
} else {
clearTimeout(lastFunc);
lastFunc = setTimeout(function() {
if ((Date.now() - lastTime) >= limit) {
fn.apply(context, args);
lastTime = Date.now();
}
}, Math.max(limit - (Date.now() - lastTime), 0));
}
};
}
// Text-based icon for maximum contrast/visibility (with SVG fallback appended)
var textIcon = '<span class="back-to-top-icon" aria-hidden="true">▲</span>';
var svgFallback = '\n <svg class="back-to-top-svg-fallback" width="24" height="24" viewBox="0 0 24 24" aria-hidden="true" focusable="false" role="img">\n <path class="filled" d="M6 14L12 8L18 14H6Z"/>\n <rect class="filled" x="11" y="14" width="2" height="6" rx="1"/>\n </svg>\n ';
function ensureSingleButton() {
var nodes = document.querySelectorAll('#' + BUTTON_ID);
if (nodes.length > 1) {
// Keep the first, remove the rest
for (var i = 1; i < nodes.length; i++) nodes[i].parentNode && nodes[i].parentNode.removeChild(nodes[i]);
}
return document.getElementById(BUTTON_ID);
}
function createOrAdoptButton() {
var btn = ensureSingleButton();
if (!btn) {
btn = document.createElement('button');
btn.id = BUTTON_ID;
btn.type = 'button';
btn.className = 'back-to-top';
btn.setAttribute('aria-label', 'Back to top');
btn.innerHTML = textIcon + svgFallback;
document.body.appendChild(btn);
} else {
// Adopt existing markup and normalize
btn.type = 'button';
btn.classList.add('back-to-top');
btn.setAttribute('aria-label', 'Back to top');
if (!btn.querySelector('.back-to-top-icon')) btn.insertAdjacentHTML('afterbegin', textIcon);
if (!btn.querySelector('.back-to-top-svg-fallback')) btn.insertAdjacentHTML('beforeend', svgFallback);
}
return btn;
}
function init() {
var button = createOrAdoptButton();
// Essential styles inline to ensure fixed positioning; centered at bottom
var computed = window.getComputedStyle(button);
var cssApplied = computed && computed.position === 'fixed';
button.style.setProperty('position', 'fixed', 'important');
button.style.setProperty('left', '50%', 'important');
button.style.removeProperty('right');
button.style.removeProperty('top');
button.style.setProperty('bottom', '16px', 'important');
button.style.setProperty('transform', 'translate(-50%, 0)', 'important');
button.style.setProperty('display', 'inline-flex', 'important');
// Baseline dimensions/appearance (let CSS handle colors/theme)
button.style.width = '48px';
button.style.height = '48px';
button.style.alignItems = 'center';
button.style.justifyContent = 'center';
button.style.borderRadius = '9999px';
button.style.setProperty('z-index', '13001', 'important');
// Track potential nested scroll containers used by the theme
var containerSelectors = ['main', '.md-content', '.md-main', '.md-main__inner', '.md-content__inner'];
var attached = new WeakSet();
var scrollContainers = [];
function findScrollContainers() {
var set = new Set();
containerSelectors.forEach(function(sel){
var els = document.querySelectorAll(sel);
els.forEach(function(el){
if (el && el !== document.body && el !== document.documentElement) set.add(el);
});
});
scrollContainers = Array.from(set);
// Attach scroll listeners to any new containers
scrollContainers.forEach(function(el){
if (!attached.has(el)) {
el.addEventListener('scroll', onScroll, { passive: true });
attached.add(el);
}
});
}
function currentScrollTop() {
// Prefer scrollingElement for cross-browser accuracy, fallback to window
var se = document.scrollingElement || document.documentElement;
var st = se ? se.scrollTop : 0;
if (st === 0 && typeof window.pageYOffset === 'number') st = window.pageYOffset;
// Also consider nested containers; take the max scrollTop among them
if (scrollContainers && scrollContainers.length) {
for (var i = 0; i < scrollContainers.length; i++) {
var el = scrollContainers[i];
if (el && typeof el.scrollTop === 'number') {
if (el.scrollTop > st) st = el.scrollTop;
}
}
}
return st;
}
function toggleVisibility() {
var st = currentScrollTop();
var show = st > THRESHOLD;
if (show) button.classList.add('visible');
else button.classList.remove('visible');
}
var onScroll = throttle(toggleVisibility, 100);
window.addEventListener('scroll', onScroll, { passive: true });
window.addEventListener('resize', onScroll);
window.addEventListener('hashchange', onScroll);
// Initial container discovery and listener wiring
findScrollContainers();
// Re-discover containers when Material swaps content dynamically
var observer = new MutationObserver(function(mutations){
var needsUpdate = false;
for (var i = 0; i < mutations.length; i++) {
var m = mutations[i];
if (m.type === 'childList') { needsUpdate = true; break; }
}
if (needsUpdate) {
findScrollContainers();
onScroll();
}
});
observer.observe(document.body, { childList: true, subtree: true });
// Initial state
button.classList.remove('visible');
toggleVisibility();
function scrollToTop(e) {
if (e) e.preventDefault();
try {
window.scrollTo({ top: 0, behavior: 'smooth' });
} catch (_) {
// Fallback for older browsers
document.documentElement.scrollTop = 0;
document.body.scrollTop = 0;
}
}
button.addEventListener('click', scrollToTop);
button.addEventListener('keydown', function(e) {
if (e.key === 'Enter' || e.key === ' ') {
e.preventDefault();
scrollToTop(e);
}
});
}
if (document.readyState === 'loading') {
document.addEventListener('DOMContentLoaded', init);
} else {
init();
}
})();
