title: jquery get only first checkbox of a tr
body: <p>I want to check if the first checkbox in a tr is selected not all the checkbox that is found in this tr.</p>
  
  <p>For the time being i have this code :</p>
  
  <pre><code>var b = false;
  $j('#tb1 td input:checkbox').each(function(){ 
        if($j(this).is(':checked')){
      b = true;
        }
  });
  </code></pre>
  
  <p>this check if there is at least one checkbox check
  but if i add this to my selector :</p>
  
  <pre><code>$j('#tb1 td input:first:checkbox').each(function(){ 
        if($j(this).is(':checked')){
      b = true;
        }
  });
  </code></pre>
  
  <p>it check for only the first row not for all the rows and only the first checkbox.
  How can i achieve this by using the "first" selector ? 
  Thanks in advance</p>