app2.js

var mraa = require("mraa");
var lcd = require('jsupm_i2clcd');

var button = new mraa.Gpio(2);
button.dir(mraa.DIR_IN);

//var led = new mraa.Pwm(3);
//led.period(1);
//led.enable(true);

var knob = new mraa.Aio(1);

var ledOn = false;
var last_push = button.read();
var readFloat = 0;

var myLCD = new lcd.Jhd1313m1(6, 0x3E, 0x62);
var clearStr   = "                         ";

setInterval(function() {
  var push = button.read();
  if(push && !last_push) {
   ledOn = !ledOn;   
  }
  last_push = push;
  if (ledOn) {
    readFloat = (knob.readFloat()*10).toFixed(2);
    myLCD.setColor(0, 255, 0);
    myLCD.setCursor(0,0);   
    myLCD.write(clearStr);
    myLCD.setCursor(0,0);
    myLCD.write("Ambient: " + readFloat);
  } else {
    readFloat = 0;
    myLCD.setColor(20, 20, 20);
    myLCD.setCursor(0,0);   
    myLCD.write(clearStr);
    myLCD.setCursor(0,0);
    myLCD.write("Ambient: OFF");
  } 
}, 100);