title: Node.js Gmail API how can I access the contents of an email?
body: <p>I'm a noob to Node.js and the Google Gmail API. However, I am familiar with client-side JavaScript. I was able to analyze the code and understand it.</p>
  
  <p>I was able to follow this guide (<a href="https://developers.google.com/gmail/api/quickstart/nodejs" rel="nofollow noreferrer">https://developers.google.com/gmail/api/quickstart/nodejs</a>) to access the labels in my Gmail account (code below):</p>
  
  <pre><code>var fs = require('fs');
  var readline = require('readline');
  var google = require('googleapis');
  var googleAuth = require('google-auth-library');
  
  // If modifying these scopes, delete your previously saved credentials
  // at ~/.credentials/gmail-nodejs-quickstart.json
  var SCOPES = ['https://www.googleapis.com/auth/gmail.readonly'];
  var TOKEN_DIR = (process.env.HOME || process.env.HOMEPATH ||
      process.env.USERPROFILE) + '/.credentials/';
  var TOKEN_PATH = TOKEN_DIR + 'gmail-nodejs-quickstart.json';
  
  // 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), listLabels);
  });
  
  /**
   * 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) {
    try {
      fs.mkdirSync(TOKEN_DIR);
    } catch (err) {
      if (err.code != 'EEXIST') {
        throw err;
      }
    }
    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 &lt; labels.length; i++) {
          var label = labels[i];
          console.log('- %s', label.name);
        }
      }
    });
  }
  </code></pre>
  
  <p>According to (<a href="https://developers.google.com/gmail/api/v1/reference/users/messages/delete#javascript" rel="nofollow noreferrer">https://developers.google.com/gmail/api/v1/reference/users/messages/delete#javascript</a>), this code will allow me to read emails. However, while the page (linked above) explains the parameters for the functions below, it doesn't explain how to get the message ID. The function asks for an integer (I guess) to determine which message to return. However, there is no information explaining how to get the <code>message ID</code> in the first place. Am I supposed to use a loop and get all the emails and then figure out which I want? What should <code>message ID</code> be? Code below:</p>
  
  <pre><code>/**
   * Delete Message with given ID.
   *
   * @param  {String} userId User's email address. The special value 'me'
   * can be used to indicate the authenticated user.
   * @param  {String} messageId ID of Message to delete.
   */
  function deleteMessage(userId, messageId) {
    var request = gapi.client.gmail.users.messages.delete({
      'userId': userId,
      'id': messageId
    });
    request.execute(
      function(resp) { });
  }
  </code></pre>
  
  <p>Thank you.</p>