How to integrate a jade variable instead of a class?

Question

Pug

How to integrate a jade variable instead of a class?
a.link(href='').#{active}
doesn't work like this
The variable itself is declared above like this - var active = "active"
Error due to a.link(href='').#{active} like this Unexpected token `interpolation` expected `text`, `code`, `:`, `newline` or `eos`
UPD
a.link(href='',class='#{active}')
like this