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 }()); 50
