BTW, do you know the code patten for `this`? I see you use lot of global variable `self` to avoid `bind(this)`. If you only have a small scoop for asynchronies callback block, I agree you to use `var self = this` . You might need to access it one or two times. Otherwise, you access `self` anywhere in `nfc_handover.js`, it make the code older less. And let the pattern `this` be useless. Are you able to avoid access `self` variable anywhere?