//while循环
 <script type="text/javascript">
i = 1;
while (i <= 6)
{
document.write("<h" + i+">这是标题"+i);
document.write("</h"+i+">");
i++;
}
</script>

 //do_whilel循环
<script type="text/javascript">
i = 1;
do
{
document.write("<h" + i+">这是标题"+i);
document.write("</h"+i+">");
i++;
}
while(i<=6);
</script>

//for循环 
 <script type="text/javascript">
for(i=1;i<=6;i++)
{
  document.write("<h"+i+">这是标题"+i);
  document.write("</h"+i+">");
}
</script>