本文实例讲述了JS控制层作圆周运动的方法。分享给大家供大家参考，具体如下：
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> <title>圆周运动</title> <script type = "text/javascript"> window.onload = function(){ var ctrlBtn = $id("ctrl"); var isMove = true; oM = null; ctrlBtn.onclick = function(){ if(isMove){ moveByCircle(); }else{ clearInterval(oM); } isMove = !isMove; } } function moveByCircle(){ var bacL = parseInt($id("clockBac").style.left); var bacT = parseInt($id("clockBac").style.top); var bacW = parseInt($id("clockBac").style.width); var bacH = parseInt($id("clockBac").style.height); var initL = bacL+bacW/2; var initT = bacT+bacH/2; var step = 0; var r = 65; $id("tt").style.left = initL+"px"; $id("tt").style.top = initT+"px"; var l = parseInt($id("tt").style.left); var t = parseInt($id("tt").style.top); oM = window.setInterval(function(){ if (step == 360) { step = 1; } $id("tt").style.left = (l + r * Math.sin(step)) + "px"; $id("tt").style.top = (t - r * Math.cos(step)) + "px"; step += 3.14/30; var d = new Date(); var hh = d.getHours(); var mm = d.getMinutes(); var ss = d.getSeconds(); $id("ctrl").value = hh+":"+mm+":"+ss; }, 1000); } function $id(id){ return document.getElementById(id); } </script> </head> <body> <div id = "tt" style ="width:10px;height:10px;background:red;position:absolute;top:105px;left:130px;"></div> <input type = "button" id = "ctrl" style = "width:100px;position:absolute;"/> <img src = "../img/clock.jpg" id = "clockBac" style ="width:200px;height:200px;top:100px;left:100px;position:absolute;z-index:-999"/> </body> </html>
希望本文所述对大家JavaScript程序设计有所帮助。