t = setTimeout("S()",500); 为什么要赋值给t而不直接写成 setTimeout("S()",500);

Question

<script type="text/javascript">function startTime(){var today=new Date()var h=today.getHours()var m=today.getMinutes()var s=today.getSeconds()// add a zero in front of numbers<10m=checkTime(m)s=checkTime(s)document.getElementById('txt').innerHTML=h+":"+m+":"+st = setTimeout('startTime()',500)//t = setTimeout("S()",500);  为什么要赋值给t而不直接写成setTimeout("S()",500);}function checkTime(i){if (i<10)   {i="0" + i}  return i}</script>

Answer 1

可以直接写延时器,而把定时器赋值给 t, 是为了方便以后的处理,例如,后面若想清除延时器,只需写 clearTimeout(t),比再写一遍延时器,代码量小了很多.

Answer 2

把定时器储存在一个变量里面，方便后面调用