Fetch all mail by google api in nodejs

To fetch all mail using the Google API in Node.js, you will need to follow these steps:

1. Set up a project in the Google Developer Console and enable the Gmail API. You will need to create credentials for your application and download the client secret file.

2. Install the google-auth-library, google-auth-oauth2, and googleapis npm packages. These libraries will allow you to authenticate with the Google API and make authorized requests.

3. Load the client secret file and use it to authenticate your application. This will allow you to access the Gmail API on behalf of a user.

4. Use the googleapis library to make a request to the Gmail API to retrieve the list of messages. You can use the list method of the gmail.users().messages object to do this.

5. Iterate through the list of messages and use the get method of the gmail.users().messages object to retrieve the full details of each message.

Here is some sample code that demonstrates how to accomplish this:

const fs = require('fs');
const readline = require('readline');
const {google} = require('googleapis');

// If modifying these SCOPES, delete token.json.
const SCOPES = ['https://www.googleapis.com/auth/gmail.readonly'];
const TOKEN_PATH = 'token.json';

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

/**
 * 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) {
  const {client_secret, client_id, redirect_uris} = credentials.installed;
  const oAuth2Client = new google.auth.OAuth2(
      client_id, client_secret, redirect_uris[0]);

  // Check if we have previously stored a token.
  fs.readFile(TOKEN_PATH, (err, token) => {
    if (err) return getNewToken(oAuth2Client, callback);
    oAuth2Client.setCredentials(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 for the authorized client.
 */
function getNewToken(oAuth2Client, callback) {
  const authUrl = oAuth2Client.generateAuthUrl({
    access_type: 'offline',
    scope: SCOPES,
  });
  console.log('Authorize this app by visiting this url:', authUrl);
  const rl