Johns was set to become a restricted free agent at the conclusion of this season.
Johns, 23, has appeared in four games for Dallas this season, recording one goal and two penalty minutes. He made his NHL debut on March 11 against the Chicago Blackhawks, registering three hits and three blocked shots in 17:27.
On Thursday night, Johns scored his first career NHL goal to tie the game in the third period in the Stars' 4-3 win over the Tampa Bay Lightning.
Johns was originally selected by Chicago in the second round (60th overall) of the 2010 NHL draft and was acquired by Dallas via trade on July 10, 2015.
The Chicago Blackhawks assigned defenseman David Rundblad to the Rockford IceHogs of the American Hockey League.
Rundblad, 25, was on loan by the Blackhawks to the ZSC Lions of Switzerland's National League A.
Rundblad has notched two assists in nine games with the Blackhawks this season. The native of Lycksele, Sweden registered 16 points (three goals, 13 assists) in 63 regular-season games over three seasons with Chicago (2013-15). He also appeared in five Stanley Cup playoff games last season.
Over his five-year NHL career, Rundblad has scored 25 points (four goals, 21 assists) in 113 career games with Ottawa (2011-12), Phoenix (2011-2014) and Chicago (2014-16).
The Buffalo Sabres recalled defenseman Chad Ruhwedel and goaltender Nathan Lieuwen from the Rochester Americans of the American Hockey League.
Ruhwedel, 25, has totaled 22 points in 46 AHL games this season, leading all Rochester defensemen with eight goals. He has 11 points (four goals, seven assists) in his last 12 games.
The San Diego native has appeared in 32 career games with the Sabres since making his NHL debut in the 2012-13 season and will join the team on his first recall this season.
The 6-4, 200-pound Lieuwen, 24, joins the Sabres on his second recall of the season after serving as the team's backup goalie for five games in October.
In 26 AHL games this season, he has compiled a 14-10-1 record with a .911 save percentage and 2.86 goals-against average. A native of Abbotsford, British Columbia and the Sabres' sixth-round pick in the 2011 NHL draft, Lieuwen played in seven games for the Sabres during the 2013-14 season, posting a 1-4-0 record with a .906 save percentage and 2.98 goals-against average.
The New Jersey Devils recalled forward Brian O'Neill on an emergency basis from Albany of the AHL.
O'Neill, 27, has two assists and eight penalty minutes in 22 games with the Devils this season. He has 23 points (nine goals, 14 assists) and four penalty minutes in 31 games with Albany.))