2007-08: Janosik scored 4 goals with 15 assists and had 38 PIM in 42 games for HC Liberec in the U-18 Czech Junior League.
2008-09: Janosik split the season between HC Liberec's U-18 and U-20 teams in Czech juniors. He scored 1 goal with 8 assists and 12 PIM in 22 games for the U-20 squad and scored 7 goals with 19 assists and 39 PIM in 20 games at the U-18 level. Janosik represented Slovakia in the WJC U-18 tournament; scoring 1 goal with 4 assists and 2 PIM in six games as Slovakia finished seventh in the ten-team tournament. Janosik was selected in the first round (46th overall) by Gatineau Olympiques in the 2009 CHL Import Draft.
2009-10: Janosik fit in well with Gatineau in his first year of North American junior hockey. He was the second-leading scorer among Gatineau defensemen with 9 goals and 26 assists and his +14 plus/minus rating was only one point less than Olympiques' leading scorer Tye McGinn's +15. Gatineau finished third in the Western Division and defeated Montreal in seven games in the first round of playoff before falling to eventual league runner-up Saint John in four straight in the second round. Janosik scored 5 goals (four on the power play), with 2 assists and was -6 with 4 PIM. He suffered a concussion in Game Three vs. Saint John and didn't play in the final game.
2010-11: Janosik skated in 60 of 68 games for the Gatineau Olympiques in his second year with the club and represented Slovakia at the 2011 U20 World Junior Championship. Janosik scored 7 goals with 25 assists and was +17 with 37 PMs on a Gatineau team that finished third in the competitive West Division before advancing to the QMJHL's playoff finals. He was -3 in 24 playoff games with 5 goals, 4 assists and 12 PMs. Janosik led eighth-place Slovakia with five assists in six games and was +1 with 2 PMs.
Janosik is a thin, young player whose game is predicated on skating, moving the puck and creating scoring opportunities for players around him. He relies on his speed, quickness and hockey sense to compensate for a lack of bulk and strength. He can be overpowered physically at times due to his size and lack of physical development but anticipates well to keep himself out of one-on-one situations. Janosik's defensive play and positioning are sometimes erratic. Janosik should improve the velocity of his shot and his ability to stick handle in tight spaces as he adds muscle and strength to his frame. Currently lacking in physical and technical skills, Janosik is a prospect because of his offensive instincts, creativity, and willingness to attack.
Janosik will return to Gatineau for his second season of junior hockey following Tampa Bay's training camp. Still very raw in terms of physical development and positional play, he has the potential to be a puck-moving defenseman who is at his best in transitional play at the NHL level. Coaches will tell you that it's easier to teach the defensive side of the game and develop strength than to develop playmaking players who are able to execute and make decisions at high speed. Janosik has the ability to do the latter.