npm install gpio

var gpio = require("gpio");

// Calling export with a pin number will export that header and return a gpio header instance
var gpio4 = gpio.export(4, {
   // When you export a pin, the default direction is out. This allows you to set
   // the pin value to either LOW or HIGH (3.3V) from your program.
   direction: gpio.DIRECTION.OUT,

   // set the time interval (ms) between each read when watching for value changes
   // note: this is default to 100, setting value too low will cause high CPU usage
   interval: 200,

   // Due to the asynchronous nature of exporting a header, you may not be able to
   // read or write to the header right away. Place your logic in this ready
   // function to guarantee everything will get fired properly
   ready: function() {
   }
});

var gpio = require("gpio");
var gpio4 = gpio.export(4, {
   direction: gpio.DIRECTION.IN,
   ready: function() {
   }
});

// sets pin to high
gpio4.set();

// sets pin to low (can also call gpio4.reset())
gpio4.set(0);

// Since setting a value happens asynchronously, this method also takes a
// callback argument which will get fired after the value is set
gpio4.set(function() {
   console.log(gpio4.value);    // should log 1
});
gpio4.set(0, function() {
   console.log(gpio4.value);    // should log 0
});

// unexport program when done
gpio4.unexport();

// bind to the "change" event
gpio4.on("change", function(val) {
   // value will report either 1 or 0 (number) when the value changes
   console.log(val)
});
      
// you can bind multiple events
var processPin4 = function(val) { console.log(val); };
gpio4.on("change", processPin4);
            
// unbind a particular callback from the "change" event
gpio4.removeListener("change", processPin4);
      
// unbind all callbacks from the "change" event
gpio4.removeAllListeners("change");
      
// you can also manually change the direction anytime after instantiation            
gpio4.setDirection(gpio.DIRECTION.OUT);
gpio4.setDirection(gpio.DIRECTION.IN);

var gpio = require("gpio");
var gpio22, gpio4, intervalTimer;

// Flashing lights if LED connected to GPIO22
gpio22 = gpio.export(22, {
   ready: function() {
      intervalTimer = setInterval(function() {
         gpio22.set();
         setTimeout(function() { gpio22.reset(); }, 500);
      }, 1000);
   }
});

// Lets assume a different LED is hooked up to pin 4, the following code 
// will make that LED blink inversely with LED from pin 22 
gpio4 = gpio.export(4, {
   ready: function() {
      // bind to gpio22's change event
      gpio22.on("change", function(val) {
         gpio4.set(1 - val); // set gpio4 to the opposite value
      });
   }
});

// reset the headers and unexport after 10 seconds
setTimeout(function() {
   clearInterval(intervalTimer);          // stops the voltage cycling
   gpio22.removeAllListeners('change');   // unbinds change event
   gpio22.reset();                        // sets header to low
   gpio22.unexport();                     // unexport the header
   
   gpio4.reset();
   gpio4.unexport(function() {
      // unexport takes a callback which gets fired as soon as unexporting is done
      process.exit(); // exits your node program
   });
}, 10000)