Japan had been in the geopolitical picture, with consequent press coverage since the end of the Boxer Rebellion in 1900 or earlier. In 1905 the Japanese showed they could defeat a European power in the Russo-Japanese war using modern equipment. Since Theodore Roosevelt hosted the peace conference, (winning a nobel peace prize) the idea of Japan as a modern potent state would have been part of U.S. mass politics as well.

However, negative, racist, stereotypes of Japan did exist and were widespread before WWII. Japanese were depicted and thought of as imitating rather than creating technological innovation. Common stereotypes depicted Japanese people as physically and mentally inferior, (especially in eyesight for some reason). As such, it was assumed that the Japanese would always be slightly behind technologically, regardless of their achievements since 1871. The quality of the Japanese Naval and Air Forces, Zero fighter aircraft in particular, were therefore extremely shocking to Americans in 1941-2.

source: Dower, John "War without Mercy" 1986