drive_led_with_button.js

var fs = require('fs');

var button_gpio = 17; // maps to digital PIN5 on the board
var led_gpio    = 27; // maps to digital PIN7

var fileOptions = {encoding: 'ascii'};

var exportGpio = function(gpio_nr) {
  fs.writeFile('/sys/class/gpio/export', gpio_nr, fileOptions, function (err) {
    if (err) { console.log("Couldn't export %d, probably already exported.", gpio_nr); }
  });
};

var setGpioDirection = function(gpio_nr, direction) {
  fs.writeFile("/sys/class/gpio/gpio" + gpio_nr + "/direction", direction, fileOptions, function (err) {
    if (err) { console.log("Could'd set gpio" + gpio_nr + " direction to " + direction + " - probably gpio not available via sysfs"); }
  });
}

var setGpioIn = function(gpio_nr) {
  setGpioDirection(gpio_nr, 'in');
}

var setGpioOut = function(gpio_nr) {
  setGpioDirection(gpio_nr, 'out');
}

// pass callback to process data asynchroniously
var readGpio = function(gpio_nr, callback) {
  var value;
  
  fs.readFile("/sys/class/gpio/gpio" + gpio_nr + "/value", fileOptions, function(err, data) {
    if (err) { console.log("Error reading gpio" + gpio_nr); }
    value = data;
    callback(data);
  });
  return value;
};

var writeGpio = function(gpio_nr, value) {
  fs.writeFile("/sys/class/gpio/gpio" + gpio_nr + "/value", value, fileOptions, function(err, data) {
    if (err) { console.log("Writing " + gpio_nr + " " + value); }
  });
};

exportGpio(led_gpio);
exportGpio(button_gpio);

setGpioOut(led_gpio);
setGpioIn(button_gpio);

// repeat reading/writing in a loop
setInterval(function() {
  readGpio(button_gpio, function(data) {
    writeGpio(led_gpio, data);
  });
}, 1000);

Button Sketch例のnode版です。
注意）ボタン用Pinは２番ではなく、５番です。（GPIO mapping）