npm start

        var fs = require('fs');
        var readline = require('readline');
        var google = require('googleapis');
        var googleAuth = require('google-auth-library');

        var express = require('express');
        var router = express.Router();

        router.get('/', function(req, res, next) {
          res.render('gmail', { title: 'GMail is abled now..., see log' });
        });


        var SCOPES = ['https://mail.google.com/'];

        var TOKEN_PATH = 'gmail-api-token.json'; // need token 
        // https://console.developers.google.com/apis/dashboard


        // Load client secrets from a local file.
        fs.readFile('client_secret.json', function processClientSecrets(err, content) {
            if (err) {
                console.log('Error loading client secret file: ' + err);
                return;
            }
            // Authorize a client with the loaded credentials, then call the
            // Gmail API.
            authorize(JSON.parse(content), sendMessage);
        });

        /**
         * Create an OAuth2 client with the given credentials, and then execute the
         * given callback function.
         *
         * param {Object} credentials The authorization client credentials.
         * param {function} callback The callback to call with the authorized client.
         */
        function authorize(credentials, callback) {
            var clientSecret = credentials.installed.client_secret;
            var clientId = credentials.installed.client_id;
            var redirectUrl = credentials.installed.redirect_uris[0];
            var auth = new googleAuth();
            var oauth2Client = new auth.OAuth2(clientId, clientSecret, redirectUrl);

            // Check if we have previously stored a token.
            fs.readFile(TOKEN_PATH, function (err, token) {
                if (err) {
                    getNewToken(oauth2Client, callback);
                } else {
                    oauth2Client.credentials = JSON.parse(token);
                    callback(oauth2Client);
                }
            });
        }

        /**
         * Get and store new token after prompting for user authorization, and then
         * execute the given callback with the authorized OAuth2 client.
         *
         * //param {google.auth.OAuth2} oauth2Client The OAuth2 client to get token for.
         * //param {getEventsCallback} callback The callback to call with the authorized
         *     client.
         */
        function getNewToken(oauth2Client, callback) {
            var authUrl = oauth2Client.generateAuthUrl({
                access_type: 'offline',
                scope: SCOPES
            });
            console.log('Authorize this app by visiting this url: ', authUrl);
            var rl = readline.createInterface({
                input: process.stdin,
                output: process.stdout
            });
            rl.question('Enter the code from that page here: ', function (code) {
                rl.close();
                oauth2Client.getToken(code, function (err, token) {
                    if (err) {
                        console.log('Error while trying to retrieve access token', err);
                        return;
                    }
                    oauth2Client.credentials = token;
                    storeToken(token);
                    callback(oauth2Client);
                });
            });
        }

        /**
         * Store token to disk be used in later program executions.
         *
         * //param {Object} token The token to store to disk.
         */
        function storeToken(token) {
            fs.writeFile(TOKEN_PATH, JSON.stringify(token));
            console.log('Token stored to ' + TOKEN_PATH);
        }

        /**
         * Lists the labels in the user's account.
         *
         * @param {google.auth.OAuth2} auth An authorized OAuth2 client.
         */
        function listLabels(auth) {
            var gmail = google.gmail('v1');
            gmail.users.labels.list({
                auth: auth,
                userId: 'me',
            }, function (err, response) {
                if (err) {
                    console.log('The API returned an error: ' + err);
                    return;
                }
                var labels = response.labels;
                if (labels.length == 0) {
                    console.log('No labels found.');
                } else {
                    console.log('Labels:');
                    for (var i = 0; i < labels.length; i++) {
                        var label = labels[i];
                        console.log('- %s', label.name);
                    }
                }
            });
        }

        /**
         * Send Message.
         */
        function sendMessage(auth) {
            var gmail = google.gmail('v1');
            var email_lines = [];
            email_lines.push("From: [email protected]");
            email_lines.push("To:[email protected]");
            email_lines.push('Content-type: text/html;charset=utf-8');
            email_lines.push('MIME-Version: 1.0');
            email_lines.push("Subject: Gmail Sender here");
            email_lines.push("");
            email_lines.push("text text tex");
            email_lines.push("<b>bold text text </b>");

            var email = email_lines.join("\r\n").trim();

            var base64EncodedEmail = new Buffer(email).toString('base64').replace(/\+/g, '-').replace(/\//g, '_');
            console.log(base64EncodedEmail);

            function sendDone(err, response) {
                if (err) {
                    console.log('The API returned an error: ' + err);
                    return;
                }
                console.log('send mail success', response);
            }

            gmail.users.messages.send({
                auth: auth,
                userId: 'me',
                resource: {
                    raw: base64EncodedEmail
                }
            }, sendDone);
        }

        module.exports = router;