screenshot.js

var webdriver = require('selenium-webdriver');
var fs = require('fs');

var driver = new webdriver.Builder().build();

webdriver.WebDriver.prototype.saveScreenshot = function(filename) {
    return driver.takeScreenshot().then(function(data) {
        fs.writeFile(filename, data.replace(/^data:image\/png;base64,/,''), 'base64', function(err) {
            if(err) throw err;
        });
    })
};


// example usage
driver.saveScreenshot('mypage.png');