setTimeout(code,millisec) 方法用于在指定的毫秒数后调用函数或计算表达式
setInterval(code,millisec) 方法可按照指定的周期（以毫秒计）来调用函数或计算表达式
区别：setTimeout() 只执行 code 一次。如果要多次调用，请使用 setInterval() 或者让 code 自身再次调用 setTimeout()
setTimeout() 函数实现时钟的例子
<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <title>预备启动秒表</title> <script type="text/javascript"> function timedMsg() { var second = document.getElementById("second").value; var minute = document.getElementById("minute").value; var hour = document.getElementById("hour").value; second = parseInt(second); minute = parseInt(minute); hour = parseInt(hour);
var second = second + 1; if(second >59){ second = 0; minute = minute + 1; if(minute > 59){ minute = 0; hour = hour + 1; if(hour>23){ hour = 0; } } } //数据格式处理 if(second < 10){ second = "0" + second; } if(minute < 10){ minute = "0" + minute; } if(hour < 10){ hour = "0" + hour; } document.getElementById('second').value= second; document.getElementById('minute').value= minute; document.getElementById('hour').value= hour; var t = setTimeout("timedMsg();",1000); } </script> </head> <body> <button onclick="timedMsg()">预备启动秒表</button> <br> <br> 时<input type="text" name="hour" id="hour" value="00"> 分<input type="text" name="minute" id="minute" value="00"> 秒<input type="text" name="second" id="second" value="00"> </body> </html>