blob: d57a817131b3aa71c8af7c0b9332c9d4edcd61ef [file] [log] [blame]
/**
* @license
* Copyright 2019-2020 The Go Authors. All rights reserved.
* Use of this source code is governed by a BSD-style
* license that can be found in the LICENSE file.
*/
/**
* Shows a fixed element when a separate element begins to go out of view.
*/
class FixedHeaderController {
/**
* @param {Element} el
* @param {Element} fixedEl
*/
constructor(el, fixedEl) {
if (!el || !fixedEl) {
throw new Error('Must provide sentinel and fixed elements to constructor.');
}
/**
* The element to observe to determine whether to show the fixed element.
* @type {!Element}
* @private
*/
this._el = /** @type {!Element} */ (el);
/**
* The element to show when the other begins to go out of view.
* @type {!Element}
* @private
*/
this._fixedEl = /** @type {!Element} */ (fixedEl);
/**
* @type {!IntersectionObserver}
* @private
*/
this._intersectionObserver = new IntersectionObserver(
(entries, observer) => this.intersectionObserverCallback(entries, observer),
{
threshold: 1.0,
}
);
this._intersectionObserver.observe(this._el);
// Fixed positioning on Safari iOS is very broken, and without this hack,
// focusing on the overflow menu will cause all content to scroll.
// The -webkit-overflow-scroll CSS property is only available on mobile
// Safari, so check for it and set the appropriate style to fix this.
if (window.getComputedStyle(document.body)['-webkit-overflow-scrolling'] !== undefined) {
[document.documentElement, document.body].forEach(el => {
el.style.overflow = 'auto';
});
}
}
/**
* @param {!Array<IntersectionObserverEntry>} entries
* @param {!IntersectionObserver} observer
* @private
*/
intersectionObserverCallback(entries, observer) {
entries.forEach(entry => {
this._fixedEl.setAttribute('aria-hidden', entry.isIntersecting);
});
}
}