The novel sometimes uses dramatic irony to emphasize Jane's relative naïveté when she is young. For example, in Chapter 11, Jane arrives at Thornfield and mistakes Mrs. Fairfax for her new employer:
‘She treats me like a visitor,’ thought I. ‘I little expected such a reception; I anticipated only coldness and stiffness: this is not like what I have heard of the treatment of governesses; but I must not exult too soon.’
This is Jane's first governess position after leaving Lowood charity school, and she has been expecting to feel like an outsider. As a person who must work for her living, Jane is decidedly below the social status of anyone who owns Thornfield and can afford to hire help. Mrs. Fairfax treats Jane more kindly than she expected her new employer to treat her, and so she is filled with the hope that her position as governess will be something more than a job. An orphan who has long searched for belonging, Jane tamps down her own "exultation" that she has at last found a family that will welcome her with warmth, respect, and open arms. The situation seems too good to be true.
In fact, it is too good to be true. The astute reader can guess from context clues that Mrs. Fairfax is not Jane's employer, but rather another employee at Thornfield. The owner of the manor house would not be wearing servant's clothes when Jane met her, as Mrs. Fairfax is. Nor would she take Jane's shawl, serve her food, or pull out a set of housewife's keys. The narrator lets the reader in on this little secret from the younger Jane to emphasize that Jane has a lot to learn about markers of social status and the way power dynamics function outside of Lowood.
Later in Chapter 11, dramatic irony continues when the narrator recalls being excited about the days ahead of her:
My faculties, roused by the change of scene, the new field offered to hope, seemed all astir. I cannot precisely define what they expected, but it was something pleasant: not perhaps that day or that day month, but at an indefinite future period.
This is a bit of a joke about Jane as a literary character. Clearly, she did not realize at the time that she was in a gothic novel, destined for gloomy days, secrets, doomed love, and dangerous encounters with a woman locked in the attic. The narrator knows what is to come, and the reader is presumed familiar enough with gothic tropes to be able to spot the irony. Still, the naïve Jane is not altogether wrong in her prediction. The novel does have a happy ending that comes "at an indefinite future period." Thornfield brings a great deal of unexpected unpleasantness into Jane's life, but it also sets her up for the marriage she will eventually choose. The lesson she has not yet learned in this scene, and which Brontë seems intent on exploring, is that happiness pays off the most when it is attained through tribulation.