help, please, understanding my problem

I have a PHP page that has require_once("genMyOverlay.js.php"); . . . echo "<body>"; echo "<script language=\"JavaScript\">doit(\"mydiv\");</script><br>"; echo "</body>"; genMyOverlay.js.php contains: createDiv() (see below) that creates a <DIV ID="mydiv"> and sets it up to overlay a portion of the wbe page and doit()starts it off. invoke the web page once and it works like it should. invoke the web page a second time (and thereafter until a new session) and it gets error: "doit is not defined" view the source (at the client browser) and it is identical both (all) times can anyone please help me understand what is happening? genMyOverlay.js.php contains <script language="PHP"> echo "<script language=\"JavaScript\">"; echo "function createDiv()"; echo " {"; . . . echo " }"; echo "function doit(ElementID)"; echo " {"; echo " creatDIV()"; . . . echo " }"; echo "</script>"; </script>