Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
Ironic
Crane's irony isn't a ha-ha kind of irony. Like the naturalist that he is, Crane portrays life in all of its degradations and disappointments. From the novel's opening lines, we know that these people live in a brutal environment, and it's clear that the narrator isn't going to soften the blow one bit. Because of this, it's always clear that, like the narrator, readers understand that things aren't going to go well. If anything, then, the joke's on the characters—hence the ironic tone. Look at this passage for instance:
"An' wid all deh bringin' up she had, how could she?" moaningly she asked of her son. "Wid all deh talkin' wid her I did an' deh t'ings I tol' her to remember? When a girl is bringed up deh way I bringed up Maggie, how kin she go teh deh devil?"
Jimmie was transfixed by these questions. He could not conceive how under the circumstances his mother's daughter and his sister could have been so wicked. (13.4–5)
Okay, so this is Mom lamenting Maggie's moral decline to Jimmie. Instead of joining these two in their bafflement as to how Maggie's turned out the way she has, though, Mom and Jimmie both come across—at best—as kind of stupid. It is clear at every turn that Maggie has pretty much nothing to hope for and no solid options, so as readers, we feel sorry for the girl. When we see Mom and Jimmie unable to make sense of Maggie, though, we kind of sneer at them—they may think they understand the way the world works, but clearly they don't.