ser.write(setup + gap + cls + text + barcode + print_cmd) ser.close() esc = b'\x1b' ser.write(esc + b'@') # Initialize ser.write(esc + b'd\x04') # Feed 4 lines ser.write(b'My Store\nProduct: Label\n') # Text ser.write(esc + b'k\x04\x0a\x00') # Print barcode (code128) ser.write(b'\n\n\n') ser.write(esc + b'm') # Cut (if cutter present) 4.3 WebUSB / JavaScript (Browser) For web apps (Chrome/Edge):