请教一下js无缝轮播的问题 - 知否问答 - 万象云+社区

<!DOCTYPE html> <html> <head> <meta charset="UTF-8"> <title>焦点轮播图</title> <style type="text/css"> *{ margin: 0; padding: 0; text-decoration: none;} body { padding: 20px;} #container { width: 600px; height: 400px; border: 3px solid #333; overflow: hidden; position: relative;} #list { width: 4900px; height: 400px; position: absolute; z-index: 1;} #list img { float: left;} #buttons { position: absolute; height: 10px; width: 100px; z-index: 2; bottom: 20px; left: 250px;} #buttons span { cursor: pointer; float: left; border: 1px solid #fff; width: 10px; height: 10px; border-radius: 50%; background: #333; margin-right: 5px;} #buttons .on { background: orangered;} .arrow { cursor: pointer; display: none; line-height: 39px; text-align: center; font-size: 36px; font-weight: bold; width: 40px; height: 40px; position: absolute; z-index: 2; top: 180px; background-color: RGBA(0,0,0,.3); color: #fff;} .arrow:hover { background-color: RGBA(0,0,0,.7);} #container:hover .arrow { display: block;} #prev { left: 20px;} #next { right: 20px;} </style> <script type="text/javascript"> window.onload = function () { var container = document.getElementById('container'); var list = document.getElementById('list'); var buttons = document.getElementById('buttons').getElementsByTagName('span'); var prev = document.getElementById('prev'); var next = document.getElementById('next'); var index = 1; var len = 5; var animated = false; var interval = 3000; var timer; function animate (offset) { if (offset == 0) { return; } animated = true; var time = 300; var inteval = 10; var speed = offset/(time/inteval); var left = parseInt(list.style.left) + offset; var go = function (){ if ( (speed > 0 && parseInt(list.style.left) < left) || (speed < 0 && parseInt(list.style.left) > left)) { list.style.left = parseInt(list.style.left) + speed + 'px'; setTimeout(go, inteval); } else { list.style.left = left + 'px'; if(left>-600){ list.style.left = -600 * len + 'px'; } if(left<(-600 * len)) { list.style.left = '-600px'; } animated = false; } } go(); } function showButton() { for (var i = 0; i < buttons.length ; i++) { if( buttons[i].className == 'on'){ buttons[i].className = ''; break; } } buttons[index - 1].className = 'on'; } function play() { timer = setTimeout(function () { next.onclick(); play(); }, interval); } function stop() { clearTimeout(timer); } next.onclick = function () { if (animated) { return; } if (index == 5) { index = 1; } else { index += 1; } animate(-600); showButton(); } prev.onclick = function () { if (animated) { return; } if (index == 1) { index = 5; } else { index -= 1; } animate(600); showButton(); } for (var i = 0; i < buttons.length; i++) { buttons[i].onclick = function () { if (animated) { return; } if(this.className == 'on') { return; } var myIndex = parseInt(this.getAttribute('index')); var offset = -600 * (myIndex - index); animate(offset); index = myIndex; showButton(); } } container.onmouseover = stop; container.onmouseout = play; play(); } </script> </head> <body> <div id="container"> <div id="list" style="left: -600px;"> <img src="img/5.jpg" alt="1"/> <img src="img/1.jpg" alt="1"/> <img src="img/2.jpg" alt="2"/> <img src="img/3.jpg" alt="3"/> <img src="img/4.jpg" alt="4"/> <img src="img/5.jpg" alt="5"/> <img src="img/1.jpg" alt="5"/> </div> <div id="buttons"> <span index="1" class="on"></span> <span index="2"></span> <span index="3"></span> <span index="4"></span> <span index="5"></span> </div> <a href="javascript:;" id="prev" class="arrow"><</a> <a href="javascript:;" id="next" class="arrow">></a> </div> </body> </html> 小弟刚学js看到这个轮播有两个地方不懂 1.多加的那两张图5和1有什么用？就直接用5张图不是也可以判断当list.style.left<0时候变list.style.left=3000px；left>3000px的时候list.style.left=0？ 2.还有最后一张滑倒第一张的时候为什么可以无缝啊我还是理解不了，left从-3000变到-600不应该是倒退回第一张吗？是因为加的那两张图的关系吗？可是。list.style.left直接从-3000变成-600了啊更不滑不到-3600这个位置上啊（第七张图）。那么它是如何实现的顺滑而不是倒滑到第一张呢？小弟愚钝望点波

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