sketch.js

/*
  2 serial port test. Put the Arduino analogReadSerial sketch
  on two Arduinos and connect them to your computer using 2
  USB ports. Note the port names and change firstPort and
  secondPort below to match. Then run this sketch. You should see
  data coming in from both ports independently.
  
*/

var serial1 = new p5.SerialPort();
var serial2 = new p5.SerialPort();
var firstPort = '/dev/cu.usbmodem14111';
var secondPort = '/dev/cu.usbmodem141431';
var input1 = '';
var input2 = '';

function setup() {
  createCanvas(400, 300);
  serial1.on('data', serialEvent);
  serial1.on('error', serialError);
  serial2.on('data', serial2Event);
  serial2.on('error', serial2Error);
  
  serial1.open(firstPort);
  serial2.open(secondPort);
}

function draw() {
  background(0x23, 0x76, 0xF3);
  fill(255);
  text("data from serial port 1:" + input1, 30, 30);
  text("data from serial port 2: " + input2, 30, 90);
}

function serialEvent(){
  data = serial1.readStringUntil('\r\n');
  if (data.length > 0){
      input1 = data;
    }
}

function serialError(err) {
  println("error with serial port 1: " + err);
}

function serial2Event() {
    var data = serial2.readStringUntil('\r\n');
    if (data.length > 0){
      input2 = data;
    }
}

function serial2Error(err) {
    println("error with serial port 2: " + err);

}