標籤：int osi eth enter mic 消失 元素 .com pointer
js
<!DOCTYPE html><html><head><title>返回頂部</title><style>body{margin:0; padding:0}#to_top{width:30px; height:40px; padding:20px; font:14px/20px arial; text-align:center; background:#06c; position:absolute; cursor:pointer; color:#fff}</style><script>window.onload = function(){ var oTop = document.getElementById("to_top"); var screenw = document.documentElement.clientWidth || document.body.clientWidth; var screenh = document.documentElement.clientHeight || document.body.clientHeight; oTop.style.left = screenw - oTop.offsetWidth +"px"; oTop.style.top = screenh - oTop.offsetHeight + "px"; window.onscroll = function(){ var scrolltop = document.documentElement.scrollTop || document.body.scrollTop; oTop.style.top = screenh - oTop.offsetHeight + scrolltop +"px"; } oTop.onclick = function(){ document.documentElement.scrollTop = document.body.scrollTop =0; }} </script></head><body style="height:1000px;"><h1>返回頂部</h1><div id="to_top">返回頂部</div></body></html>
要點一：document.documentElement.clientWidth || document.body.clientWidth； 獲得可視區的寬度。
後面是相容chrome。前面是相容其他瀏覽器。
要點二：oTop.style.left = screenw - oTop.offsetWidth +"px"; 當頁面載入時。讓元素的位置位於頁面最右邊。用可視區的寬度減去元素本身的寬度。
要點三：oTop.style.top = screenh - oTop.offsetHeight + scrolltop +"px"; 當頁面滾動時，元素的Y座標位置等於可視區的高度減去元素本身的高度，加上滾動距離。
要點四：document.documentElement.scrollTop = document.body.scrollTop =0; 當點擊元素時。讓頁面的滾動距離為0.寫兩個是為了相容。
jquery
<html><script src="http://ajax.microsoft.com/ajax/jQuery/jquery-1.7.2.min.js"></script><script> $(function(){ //當滾動欄的位置處於距頂部100像素下面時，跳轉連結出現。否則消失 $(function () { $(window).scroll(function(){ if ($(window).scrollTop()>100){ $("#back-to-top").fadeIn(1500); } else { $("#back-to-top").fadeOut(1500); } }); //當點擊跳轉連結後，回到頁面頂部位置 $("#back-to-top").click(function(){ $(‘body,html‘).animate({scrollTop:0},1000); return false; }); }); }); </script><body><p>1</p><p>2</p><p>3</p><p>4</p><p>5</p><p>6</p><p>7</p><p>8</p><p>9</p><p>10</p><p>11</p><p>12</p><p>13</p><p>14</p><p>15</p><p>16</p><p>17</p><p>18</p><p></p><p id="back-to-top"><a href="#top"><span></span>返回頂部</a></p></body></html>
js和jquery實現回到頂層
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