Neato revolver and welcome to the forum!
Iver Johnson was a prolific manufacturer of inexpensive guns and that is typical of their early products, though .22s are uncommon. If unmarked as to caliber it is probably actually chambered for .22 Long rather than the more powerful .22 Long Rifle and caution should be taken before attempting to shoot modern ammunition in it. The cylinder is almost certainly not heat treated and may be iron rather than steel- an IJ expert would be needed to confirm this, which Im not- but several of our members are, hopefully one comes along shortly.
The condition is excellent- most of these guns lived hard lives and show it. Especially interesting is the mainspring adjustment provision evident in the gripframe with the the panels removed. Moving the spring mount up and down in the frame grooves would change the spring tension.
IJs are known for being rather fragile and going out of cylinder time regularly. Even if its determined that modern ammo can be safely used, a competent gunsmith should check it out before attempting to shoot it.