(Please post your Ruby questions in the Ruby API subcategory.)
Is the variable a Ruby or JavaScript reference ?
What single quotation marks ?
… ie, we cannot read minds.
If Ruby, then you must use a double-quoted string in order to do interpolation.
I explained this in the other topic thread.
# Ruby
dlg.execute_script(
%[document.getElementById("#{ruby_id}").innerHTML="#{ruby_value}";]
)
I again point you to the Ruby Core primer on String literals …
https://ruby-doc.org/core-2.5.5/doc/syntax/literals_rdoc.html#label-Strings
If you are doing this within JavaScript, … (which I doubt because you said your are using a SketchUp Editor extension,) … you just use a string reference that holds string ID.