Johnny and Dallas are foils for each other in their similarities and their differences. Throughout the novel we can find parallels between the two, although they're almost polar opposites in some ways. Johnny can stand up to Dallas in a way that nobody else would dare. Dallas treats Johnny with the utmost kindness, and handles most others roughly at best. These two bring out the best in each other, in those respects.
Johnny is timid and fearful on the outside but brave and heroic on the inside, mustering his courage when circumstances demand it. Dallas is fearless on the outside but shies away from helping others. He's willing to risk his life for crime but not to help, because he feels like all of society has let him down and deserves only the same from him. Johnny has been hurt badly by life as well, but he sees helping others as the way to save himself. In a tragic similarity, Johnny and Dally both die in this novel – Johnny in the process of helping others, Dally in a hopeless frenzy of rage and grief.