Client side JavaScript not found after deployment

Hi, I'm creating a customized iWidget (Birt report), where I want to provide a button to hide/show specific information.
Based on some examples I used an HTML element (<INPUT Type="BUTTON" id="ordernumberbtn" Value="-" onClick='hidecol("ordernumberbtn", 1 )'></INPUT>) and provided a client side JavaScript function "hidecol" in a separate HTML text element via (<script>function hidecol(a,b) { window.alert("hello!");} </script>) defined prior to the input element.
In the Birt designer everything is working, but after deployment into RTC if I click on the button in the iWidget, nothing happens. Looking into the Browser console I see the following error: "ReferenceError: hidecol is not defined".
Any tips how one can make this work?