//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>