Ok, so I checked Pixl.js documentation.
I didn't get anything maybe I am just dumb.
According to Pinout https://www.espruino.com/Pixl.js#pinout of Pixl.js, there is a Note:
"Pixl.js has one available I2C, SPI and USART (and infinite software SPI and I2C). Unlike other Espruino boards, these peripherals can be used on any pin."
However, I also found additional information when I put my mouse cursor on these "!" two descriptions on D0 and D1 pins:
D0 - "Serial Console RX when Bluetooth is disconnected"
D1 - "Serial Console RX when Bluetooth is disconnected"
Moreover, "Purple boxes" show pins that are used for other functionality on the board. You should avoid using these unless you know that the marked device is not used.
I don't see "Purple Boxes, I see "Purple circles" on the PCB layout https://www.espruino.com/Pixl.js#pinout
Further below there are "Purple boxes" with "Pins not on connectors.
H0 3.3v LCD
H1 3.3v BTN1
H2 3.3v BTN2
H3 3.3v BTN3
H4 3.3v BTN4
H5 3.3v LCD
H6 3.3v LCD
H7 3.3v LCD
H8 3.3v ! LCD
H9 3.3v LCD
In conclusion I have a few pins rs-232 cables 2,3,5,7,8 ready and no idea where to put them in pixl.js