JSer was one of the first members of the Repl.it Discord server.
He was originally known as Caleb and had his profile picture set to an image of one of his friends with their eyes closed in a weird way.
He later changed his name to JSer; however, he is also known as gldanoob (this is his current Discord username).
He has always been one of the top users on the cycles leaderboard on Repl Talk and currently has about 1,175 cycles. This is more than both timchen and elias.
His most well-known contribution to Repl.it is his WebGL Rolling Sky repl. The post has obtained over 680 cycles and is one of the most successful repls to be created in the history of Repl.it. It has been used in promotional material for Repl.it, including the recent Repl from Repo promotional video (it can be seen around the 0:58 mark).
JSer has since given up on programming and has mostly vanished from the Repl.it community.