Dramatic irony can also be defined as a situation where the audience/reader and characters on stage have information which some characters on stage do not have.
This happens in A Doll's Housenear the opening of the play when Nora eats macaroons. When Torvald then asks Nora if she has been eating sweets, she lies and says she has not. Nora and the audience know this is a lie and so know more than Torvald making this an situation of dramatic irony.
It is ironic when Torvald states that he pretends Nora is in some kind of trouble and he awaits the moment he can rescue her. When in fact the truth comes out and Torvald has been given his opportunity to rescue Nora, all he is concerned with is his reputation. He yells at Nora. He insults her by calling her feather brain. He screams at her, telling her to go to her room. He is not interested in how he can rescue Nora. He is interested in how he can get out of this mess without ruining his good name.
Then when Krogstad returns the IOU document, Torvald exclaims that he is saved and that he has forgiven Nora. When Nora asks if she is saved, Torvald exclaims that she is, of course. Only moments earlier, he was furious with Nora. ironically, he did not even consider that she had borrowed the money to in fact save him.