Hi — I was trying to figure this out for a couple of days as well. It was a pain because I was working with the ipad, and the keyboard wouldn't go away after hitting enter.
There's another thread which uses the CallJS plugin to lose focus:
It didn't work for me unfortunately, but I found a cheap-ish workaround.
Once I filled my textbox, and pressed enter, I captured the data in a variable and destroyed the textbox, which immediately removed focus.
Next in the same condition, I recreated the textbox in the same position, and repopulated it with the text.