Yakisoba is one of very common noodle dish in Japan. It's cooked by stir-frying noodles with meat seafood vegetables and so on. The noodles for Yakisoba are similar to that of Ramen. Various taste of Yakisoba are offerd at many restaurants but basically it's classified into three types, Shoyu(醤油 meaning soy sauce) flavor Shio(塩 meaning salt) flavor and Sauce(ソース meaning Japanese sauce) flavor.
Yakisoba is common food in Japan. Because Yakisoba is affordable and many restaurants offer Yakisoba. In additon you can easily buy Yakisoba noodles at afforadable price at grocery stores. People stir-fry the noodles with vegitables and pork chicken hrimp and so on.
When most Japanese people mention sauce it almost always means Japanese sauce. It is said Japanese sauce is originated from the sauce in Worcestershire of England. Japanese people call this sauce Usutah sauce(ウスターソース). Maybe Usutah comes from Worcestershire. They often use this Japanese sauce when they cook Yakisoba.
