insertColGroups1.html

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<HEAD>

<SCRIPT src=tableDom.js>

</SCRIPT>

<SCRIPT>

function doIt() {

  var table = document.getElementsByTagName("TABLE")[0];

  var refCg = document.getElementsByTagName("COLGROUP")[0];

  var cg = document.createElement("COLGROUP", null);

  var col = document.createElement("COL", null);

  col.width = 100;

  cg.appendChild(col);

  col = document.createElement("COL", null);

  col.width = 200;

  cg.appendChild(col);

  table.insertBefore(cg, refCg);

</SCRIPT>

</HEAD>

<BODY onload="doIt()">

<table bgcolor=orange border>

 <colgroup>

  <col width=300>

 </colgroup>

 <tr>

  <td>100</td><td>200</td><td>300</td>

 </tr>

</table>

</BODY></HTML>