$('input').map(function () { return ($this).val() }).join is not a function?

$('input').map(function () { return ($this).val() }).join is not a function?

http://www.sfu.ca/~jdbates/tmp/jquery/201007270/

Why does this example ^ complain that .join() isn't a function, instead of displaying an alert, "foobar"?

Here's the script,

  1. jQuery(function ($)
      {
        alert($('input').map(function ()
          {
            return $(this).val();
          }).join(''));
      });