Twin_N:
If you somehow find any way to send serial data from android to arduino through js please let me know.
Why do you need to use Javascript?
It should be easy to communicate with an Arduino using Bluetooth and I believe there are Android apps that can do that. Maybe have a look at this RemoteXY link
Another fairly simple option would be to use an Arduino plus an ESP8266 WiFi module to host a simple website that your Android could connect to and display the website in the Android browser.
...R