Send a String from Arduino Uno to NodeMcu without connecting them to PC

I want to send a single String (containing sensors' data) from Arduino Uno to an esp8266 NodeMcu, without them being connected to my pc, but to power banks. Is this possible? How can I do this?

so you mean the arduino and esp8266 are physically connected together and powered independently from the PC and you want to use the esp wifi to communicate with some other device?

I have an Arduino Uno and a NodeMcu, each is connected to a different power bank (not to a PC).
I want to wire-connect them so I could send a String from the Arduino to the NodeMcu.

then connect there serial interfaces together

Does serial communication work without a PC?