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1 // Copyright 2013 The Chromium Authors. All rights reserved. | |
2 // Use of this source code is governed by a BSD-style license that can be | |
3 // found in the LICENSE file. | |
4 | |
5 // Scroll handling. | |
6 // | |
7 // Switches the sidebar between floating on the left and position:fixed | |
8 // depending on whether it's scrolled into view, and manages the scroll-to-top | |
9 // button: click logic, and when to show it. | |
10 (function() { | |
11 | |
12 var sidebar = document.getElementById('gc-sidebar'); | |
13 var scrollToTop = document.getElementById('scroll-to-top'); | |
14 var offsetTop = sidebar.offsetTop; | |
15 | |
16 function relayout() { | |
17 // Obviously, this code executes every time the window scrolls, so avoid | |
18 // putting things in here. | |
19 var isFloatingSidebar = sidebar.classList.contains('floating'); | |
20 var isShowingScrollToTop = !scrollToTop.classList.contains('hidden'); | |
21 | |
22 var floatSidebar = false; | |
23 var showScrollToTop = false; | |
24 | |
25 if (window.scrollY > offsetTop) { | |
26 // Scrolled past the top of the sidebar. | |
27 if (window.innerHeight >= sidebar.scrollHeight) { | |
28 // The whole sidebar fits in the window. Make it always visible. | |
29 floatSidebar = true; | |
30 } else { | |
31 // Whole sidebar doesn't fit, so show the scroll-to-top button instead. | |
32 showScrollToTop = true; | |
33 } | |
34 } | |
35 | |
36 if (floatSidebar != isFloatingSidebar) | |
37 sidebar.classList.toggle('floating', floatSidebar); | |
38 if (isShowingScrollToTop != showScrollToTop) | |
39 scrollToTop.classList.toggle('hidden', !showScrollToTop); | |
40 } | |
41 | |
42 window.addEventListener('scroll', relayout); | |
43 setTimeout(relayout, 0); | |
44 | |
45 scrollToTop.addEventListener('click', function() { | |
46 window.scrollTo(0, 0); | |
47 }); | |
48 | |
49 }()); | |
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