attr(name, value)の使い方

Link1 | Link2 | Link3

$("a[href^='http:']")
  .addClass("externallink")
  .attr("target", "_blank");

<a href="Link1.htm">Link1</a> | 
<a href="http://jsajax.com">Link2</a> | 
<a href="Link3.htm">Link3</a>