Serial Input to P5.js - Arduino and p5js code

Input2p5js.ino

void setup() {
 Serial.begin(9600); // initialize serial communications @ 9600
}
 
void loop() {
 int potentiometer = analogRead(A0);                  // read the input pin
 int mappedPot = map(potentiometer, 0, 1023, 0, 255); // remap the pot value to fit in 1 byte
 //Serial.write(mappedPot);                             // write mappedPot value to the serial port (1 byte)
 Serial.println(potentiometer);                // *or* use println to print out raw potentiometer value with newline as data separator
 delay(1);                                     // slight delay to stabilize the ADC
}

sketch.js

// Be sure to choose File > Import Library > p5.serialport.js from the P5 IDE main menu to load serial library

// Terminal command to install p5.serialserver:  npm install p5.serialserver
// Terminal command to start server:  node ~/node_modules/p5.serialserver/startserver.js

var serial;                            // variable to hold an instance of the serialport library
var options = { baudrate: 9600};      // set baudrate to 9600; must match Arduino baudrate
var portName = '/dev/cu.usbserial-DA00WVK6'; // fill in your serial port name here
var inData;                            // for incoming serial data
var slider;
function setup() {
  createCanvas(400, 300);          // make the canvas
  serial = new p5.SerialPort();    // make a new instance of the serialport library
  serial.on('data', serialEvent);  // callback for when new data arrives
  serial.on('error', serialError); // callback for errors
  serial.open(portName, options);           // open a serial port @ 9600 
  

}

function draw() {
  fill(255);
  if (inData){
    var mappedBackground = map(inData, 0, 1023, 0, 255);
    background(mappedBackground); 
    if (inData > 800){
      fill(0);
    }
  }
  else {
  background(0);
  }
  
  text("sensor value: " + inData, 30, 30);
  text("background value: " + mappedBackground, 30, 50);
}



function serialEvent() {
  // inData = Number(serial.read());   // can use this when just looking for 1 byte msgs from Arduino
  
  // Alternatively, read a string from the serial port, looking for new line as data separator:
  var inString = serial.readStringUntil('\r\n');
  // check to see that there's actually a string there:
  if (inString.length > 0 ) {
    // convert it to a number:
    inData = Number(inString);
  }
}


function serialError(err) {
  println('Something went wrong with the serial port. ' + err);
}