Get the last email of a tag in GAPI

I have the init gmail quickstart, but i want to be able to get the last email of a tag. The code i have is this. And i dont know what i have to do or what functions to use.

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

// If modifying these scopes, delete token.json.
const SCOPES = ['https://www.googleapis.com/auth/gmail.readonly'];
// The file token.json stores the user's access and refresh tokens, and is
// created automatically when the authorization flow completes for the first
// time.
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), 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) {
 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);
 });
}```

Solution

My understanding of the problem:

You want to retrieve the letest email in the specific label using Gmail API.
- I understood the last email of a tag in GAPI like above.
You want to achieve this using googleapis with Node.js.
You have already been able to get values from Gmail using Gmail API.

In this answer, I used the following flow.

Retrieve the email list of the label using the method of Users.messages: list in Gmail API.
Retrieve the email using the retrieved ID with the method of Users.messages: get in Gmail API.

Sample script:

In the authorization of this sample script, the quickstart for Node.js is used. Ref Before you use this script, please set the label name to const query = "label:sample";. In this case, "sample" is the label name.

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

// If modifying these scopes, delete credentials.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 Google Sheets 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) {
  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 = readline.createInterface({
    input: process.stdin,
    output: process.stdout,
  });
  rl.question("Enter the code from that page here: ", (code) => {
    rl.close();
    oAuth2Client.getToken(code, (err, token) => {
      if (err) return callback(err);
      oAuth2Client.setCredentials(token);
      // Store the token to disk for later program executions
      fs.writeFile(TOKEN_PATH, JSON.stringify(token), (err) => {
        if (err) return console.error(err);
        console.log("Token stored to", TOKEN_PATH);
      });
      callback(oAuth2Client);
    });
  });
}

function listLabels(auth) {
  const userId = "me";
  const query = "label:sample";  // Please set the label name. In this case, "sample" is the label name.

  const gmail = google.gmail({ version: "v1", auth });
  gmail.users.messages.list({ userId: userId, q: query }, (err1, res1) => {
    if (err1) {
      console.log(err1);
      return;
    }
    const id = res1.data.messages[0].id;
    gmail.users.messages.get({ userId: userId, id: id }, (err2, res2) => {
      if (err2) {
        console.log(err2);
        return;
      }
      console.log(res2.data);
    });
  });
}

Note:

In my environment, the 1st index of res1.data.messages is the latest message. If in your environment, the last index is the latest one, please modify above script.
If you want to know how to use above script, you can see the official document.

Get the last email of a tag in GAPI

Sample script:

Note:

References: