下面代码中，setTimeout中前段代码写成w就可以运行，写成"w()"就不能运行的原因是什么？

Question

 <script type="text/javascript">      window.onload= function w(){          var time=new Date();          var year=time.getFullYear();          var month=time.getMonth()+1;          var day=time.getDate();          var week=time.getDay()          var weekday=new Array();            weekday[0]="星期日";            weekday[1]="星期一";            weekday[2]="星期二";            weekday[3]="星期三";            weekday[4]="星期四";            weekday[5]="星期五";            weekday[6]="星期六";          var h=time.getHours();          var m=time.getMinutes();          var s=time.getSeconds();        document.getElementById("first1").innerHTML=year+"年"+month+"月"+day+"日"+weekday[week]+h+":"+m+":"+s;           setTimeout('w()',500)        }                 </script>

Answer 1

因为是回调函数，所以只要传函数名进去就行了。

Answer 2

‘w()’会认为是一个变量，w()则是运行该函数