Assumption: You are planning to work in c++.
I’m not sure what tools are built into the unreal engine source for networking but sockets work in c++ without concern for the platform being used to display the project. Unless I’m misunderstanding the question then the fact you are using HTML5 should be irrelevant to the networking portion of the game.
For an introduction into c/c++ networking in both UDP and TCP I recommend Beej’s Guide though the Unreal Engine may have built in stuff to make it so you don’t have to work at such a low level.