How to use the pigpio.Gpio.FALLING_EDGE function in pigpio

var buttonPin = 4
var ledPin = 17

var blynkToken = 'blynk_token_here';

// *** Start code *** //

var locked = true

//Setup servo
var Gpio = require('pigpio').Gpio,
  motor = new Gpio(motorPin, {mode: Gpio.OUTPUT}),
  button = new Gpio(buttonPin, {
    mode: Gpio.INPUT,
    pullUpDown: Gpio.PUD_DOWN,
    edge: Gpio.FALLING_EDGE
  }),
  led = new Gpio(ledPin, {mode: Gpio.OUTPUT});

//Setup blynk
var Blynk = require('blynk-library');
var blynk = new Blynk.Blynk(blynkToken);
var v0 = new blynk.VirtualPin(0);

console.log("locking door")
lockDoor()

button.on('interrupt', function (level) {
	console.log("level: " + level + " locked: " + locked)
	if (level == 0) {
		if (locked) {
			unlockDoor()