aspect N4 common casual
〜じゃう — casual contraction of 〜でしまう
〜じゃう ・ じゃう
A full written guide for 〜じゃう is on the way.
This point is mapped in the grammar tree, but its examples, formation table and usage notes haven't been written yet. The fastest way to learn it now is to meet it in real sentences inside Jengo.
See 〜じゃう in real sentences
Jengo shows 〜じゃう the way you actually meet it: inside real Japanese sentences, so it sticks instead of staying an abstract rule.
Study it in JengoSources Compiled with reference to A Dictionary of Basic Japanese Grammar.