Google Sheets addRow and Authentication

credentials.json

// Go to https://developers.google.com/sheets/api/quickstart/nodejs
// Click 'ENABLE THE GOOGLE SHEETS API'
// Download credentials.json

index.js

const {google} = require('googleapis');
const sheets_auth = require('./sheets-auth.js');

async function addRow(doc_id, row) {
  const auth = await sheets_auth.auth();

  const sheets = google.sheets({version: 'v4', auth});
  sheets.spreadsheets.values.append({
    spreadsheetId: doc_id,
    range: 'A1',
    valueInputOption: 'RAW',
    resource: {
      values: [
        row
      ],
    },
  }, (err, res) => {
    console.log(res.statusText);
  })
}

sheets-auth.js

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

const SCOPES = [
  'https://www.googleapis.com/auth/spreadsheets'
];
const TOKEN_PATH = './token.json';

const credentials = JSON.parse(fs.readFileSync('./credentials.json'));

function getCode() {
  return new Promise((resolve, reject) => {
    const rl = readline.createInterface({
      input: process.stdin,
      output: process.stdout,
    });
    return rl.question('Enter the code from that page here: ', code => {
      resolve(code)
      rl.close();
    })
  });
}

function getNewToken(oAuth2Client) {
  return new Promise(async (resolve, reject) => {
    const authUrl = oAuth2Client.generateAuthUrl({
      access_type: 'offline',
      scope: SCOPES,
    });
    console.log('Authorize this app by visiting this url:', authUrl);
    let code = await getCode();
    oAuth2Client.getToken(code, (err, token) => {
      fs.writeFileSync(TOKEN_PATH, JSON.stringify(token))
      resolve(token);
    });
  });
}

async function auth() {
  return new Promise(async (resolve, reject) => {
    let token;

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

    if(!fs.existsSync(TOKEN_PATH)) {
      token = await getNewToken(oAuth2Client);
    } else {
      token = JSON.parse(fs.readFileSync(TOKEN_PATH));
    }

    oAuth2Client.setCredentials(token);

    if(oAuth2Client.isTokenExpiring()) {
      await oAuth2Client.refreshAccessToken()
    }

    resolve(oAuth2Client);
  });
}

module.exports = {
  auth
}