Revalidate after added .is-invalid class

Question

I am validating my inputs by adding class "is-invalid" to them by jquery's addClass().

Then trying to revalidate them upon change with:

 $(".mandatory.is-invalid").on("input", function() {
       console.log("revalidate...");       
       validate($(this))
       });

However i cannot find the .mandatory.is-invalid elements by their class...