效果图：
代码
<!DOCTYPE html> <html> <head> <meta charset="UTF-8"> <title>红绿灯倒计时</title> <style> .box { width: 250px; height: 52px; padding: 15px 30px; border: 2px solid #ccc; border-radius: 16px; margin: 0 auto; } .box .count { width: 60px; color: #666; font-size: 280%; line-height: 50px; padding-left: 6px; margin-left: 5px; border: 1px solid #fff } .box div { margin-left: 5px; float: left; width: 50px; height: 50px; border-radius: 50px; border: 1px solid #666; } .gray { background-color: #eee; } .red { background-color: red; } .yellow { background-color: yellow; } .green { background-color: #26ff00; } </style> </head> <body> <div class="box"> <div id="red"></div> <div id="yellow"></div> <div id="green"></div> <div class="count" id="count"></div> </div> <script> // 获取红、黄、绿灯以及倒计时的元素对象 var lamp = { red: { obj: document.getElementById('red'), timeout: 30, style: ['red', 'gray', 'gray'], next: 'green' }, yellow: { obj: document.getElementById('yellow'), timeout: 5, style: ['gray', 'yellow', 'gray'], next: 'red' }, green: { obj: document.getElementById('green'), timeout: 35, style: ['gray', 'gray', 'green'], next: 'yellow' }, changeStyle(style) { this.red.obj.className = style[0]; this.yellow.obj.className = style[1]; this.green.obj.className = style[2]; } }; var count = { obj: document.getElementById('count'), change: function(num) { this.obj.innerHTML = (num < 10) ? ('0' + num) : num; } }; var now = lamp.green; var timeout = now.timeout; lamp.changeStyle(now.style); count.change(timeout); setInterval(function() { if(--timeout <= 0) { now = lamp[now.next]; timeout = now.timeout; lamp.changeStyle(now.style); } count.change(timeout); }, 1000); </script> </body> </html>
