test if first child

Question

I'm testing to see if a row in a table is the first child. So far I have:

    //the loop works
$('#GridFolderPopup').find('tr').each(function () {

    if ( $(this).is(:first) == true ) //this is the faulty line
    {
         $(this).addClass('GridFolderRow');
    };
});

Any suggestions?

Thanks

Answer 1

Simply asking for the first child of the table/tbody is much more efficient than testing every single row in it. The larger the table, the bigger the difference.

Therefore :

• if you want to "see if a [given] row in a table is the first child":

  if ($(a_given_row).prev().length === 0) {
      // no element before this row, so it's the first one.
  }
  

• if you want to get the first row of a table:

  // Directly ask the DOM for the first element child of the table/tbody
  var firstRow = a_given_table.firstChild;
  do {
     firstRow = firstRow.nextSibling;
  } while (firstRow.nodeType !== 1)
  
  // If you don't need to support IE8-, you can use this single line instead:
  var firstRow = a_given_table.firstChildElement;
  

  See performance comparison here: http://jsperf.com/get-first-child-element