Return resource based on length of field

I have a need to return different formatted text resources based on the length of a particular field. For instance, if the length of Field("Message") is between 160 and 1444 characters, return Resource("OnePageLetter"). Otherwise, return nothing. I've tried several things but I don't really understand Javascript very well so nothing is working.

Can anyone help?

if the length of Field("Message") is between 160 and 1444 characters, return Resource("OnePageLetter"). Otherwise, return nothing.

var len = Field("Message").length;
if (len >= 160 && len <= 1444)
 return Resource("OnePageLetter");
//else
return "";