decode a base64 encoded image file with node.js

nodejs_decode_sample.js

var fs = require('fs'),
    decode64 = require('base64').decode;

var data = fs.readFileSync('./encode.png', 'base64');
var buffer = new Buffer(data, 'base64');

fs.writeFileSync('./decode.png', decode64(buffer), 'binary')

Cannot find module 'base64'

npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! base64@2.1.0 install: node-gyp rebuild
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the base64@2.1.0 install script.