Table sorting in javascript

I have a table on which I want开发者_高级运维 to apply sorting, I downloaded the sortTable.js, included it in my asp page by <script src="sorttable.js"></script>, gave the table class as sortable and have all the headings inside <thead><th> tag, but still sorting does not seem to work. Am I missing something?

Here's the function I use:

function sortTable( table, colNum )
{
  var n = table.rows.length - 1;
  do
  {
    var newn = 0;
    for( i = 2 ; i <= n ; i++ )
    {
      if( table.rows[i-1].cells[colNum].innerHTML.toUpperCase() > table.rows[i].cells[colNum].innerHTML.toUpperCase() )
      {
        table.insertBefore( table.rows[i], table.rows[i-1] );
        newn = i;
      }
    }
    n = newn;
  }
  while( n > 0 );
}

table is the DOM table object and colNum is the column index in the table (0 based). It assumes there is a header row on the table (which wont be sorted). It will take a couple seconds to sort a large table (hundreds of rows), but smaller tables sort instantly.