var _href = $("a.directions-link").attr("href");
$("a.directions-link").attr("href", _href + '&saddr=50.1234567,-50.03452');
To loop with each()
$("a.directions-link").each(function() {
var $this = $(this);
var _href = $this.attr("href");
$this.attr("href", _href + '&saddr=50.1234567,-50.03452');
});