Also there is another way to handle HTML5 mobile keyboard:
Since Defold 1.3.7 we got the html5.set_interaction_listener. In this callback we able to use any different method to show the mobile keyboard. It should work inside browser user input event.
I’ve check this module: keyboard.lua from this thread. It’s works well inside html5 interaction callback. Probably for someone it will be a good way to handle this mobile input