No matter how far you go, you will never reach the end. :P
On a more technical note: The world is stored in chunks of several blocks and new chunks are only created when you place blocks in them. I'm not sure about the web version, but the desktop version stores the positions in 32bit, meaning at roughly 2 billion blocks from the starting location, the game would crash. But before that you would most likely see massive slowdowns (since all chunks are kept in memory) and/or a lot of graphical glitches (due to floating point imprecision) similar to what happens when you go too far in e.g. minecraft (You can look it up by the name of "Far Lands").
So, for all intents and purposes, the map is infinite.