"There" and "It" as subjects...

I read that "there" and "it" followed by a "to be" verb are often not the subjects but are instead placeholders. The sentences have a delayed subject (after the verb).

Is this true in the following sentences:
It's no use yelling at her.
There's no use yelling at her.

If "use" is the subject in both of these sentences, what do we call "it" and "there"? Dummy subjects?