var fileTypes = {
  doc: 'doc.gif',
  xls: 'xls.gif',
  pdf: 'pdf.gif'
};
 
$('a').each(function() {
 
  var $a = $(this);
  var href = $a.attr('href');
 
  if (
    (href.match(/^http/)) &&
    (! href.match(document.domain))
  ) {
 
    // use a special image for external links
    var image = 'external.gif';
 
  } else {
    // get the extension from the href
    var hrefArray = href.split('.');
    var extension = hrefArray[hrefArray.length - 1];
 
    var image = fileTypes[extension];
  }
 
  if (image) {
    $a.css({
      paddingLeft: '18px',
      background: 'transparent url("' + image + '") no-repeat center left'
    });
  }
 
});