This will not work. If you want to send a ClientSide variable 'fieldID' to a SSJS (getFieldHelp) you have to use something like the ExecuteOnServer function from Jeremy Hodge. because you have to POST this variable to the Server.
But why dont you use:
var helpContent ="#{javascript:getFieldHelp(compositeData.fieldID)}"
assuming that getFieldHelp is a SSJS function and both code snippets are in the same component. =) (maby you have to Change the # to $ to get the compositeData.)
update: I did some testing on getting the compositeData.FieldID in an CSJS onClientLoad event. What i came up with is this:
<xp:scriptBlock>
<xp:this.value><![CDATA[XSP.addOnLoad(function(){
alert("#{javascript:return compositeData.fieldId}");
});]]></xp:this.value>
</xp:scriptBlock>
I use the XSP.addOnLoad()
to execute the CSJS (onClientLoad) and inside the xp:scriptBlock
i can pass the compositeData to the client side.