Error: connect ECONNREFUSED 127.0.0.1:8000 in Express Js ( When try to Test with Postman )

I am really new to the industry and have this error when trying to check the database connection via API requests with Postman..... Please help me to settle this issue...

I just want to check the MongoDB database by sending API requests. Still I cannot identify the error and I am following a set of tutorials and this issue occurred... Anyone can help me to identify the mistake it's highly appreciated....

{ this is dummy text to avoid please add more details...

Here is my code...

const app = express();
const { MongoClient } = require('mongodb');
const PORT = process.env.PORT || 8000;

// Initialize middleware
// we used to install body parser but now it's a built in middleware
// Function of express. It parses incoming JSONpayload
// app.use(express.json({extended:false}));
app.use(express.json({ extended: false }));

// Test Routs
// app.get("/", (req,res)=>res.send("Hello Aruna !!!"));
// app.post("/", (req,res)=>res.send(`Hello ${req.body.name} `));
// app.get("/hello/:name", (req.res)=>res.send(`Hello ${req.params.name}`))

app.get('/api/articles/:name', async (req, res) => {
  try {
    const articleName = req.params.name;
    const client = await MongoClient.connect('mongodb://localhost:27017');
    const db = client.db('mernblog');
    const articlesinfo = db
      .collection('articles')
      .findOne({ name: articleName });
    res.status(200).jason(articlesinfo);
    client.close();
  } catch (error) {
    res.status(500).jason({ message: 'Error connecting to database', error });
  }
});
app.post('/api/articles/:name/add-comments', (req, res) => {
  const { username, text } = req.body;
  const articleName = req.params.name;
  articlesinfo[articleName].comments.push({ username, text });
  res.status(200).send(articlesinfo[articleName]);
});

app.post('/', (req, res) => res.send(`Hello ${req.body.name}`));
app.get('/hello/:name', (req, res) => res.send(`Hello ${req.params.name}`));

app.listen(PORT, () => console.log(`Server is running at port ${PORT}`));

You have a typo in your code: jason should be json.
Other tips, you should handle your DB connection in a separate method and change your post request since articlesinfo is not a global variable:

const app = express();
const { MongoClient } = require('mongodb');
const PORT = process.env.PORT || 8000;

const client = new MongoClient('mongodb://localhost:27017');

const connectDB = async () => {
    try {
        await client.connect();
        console.log('Successfully connected to DB')
    } catch (err) {
        await client.close();
        console.log('Error connecting to DB');
        process.exit(1);
    }
}

// Initialize middleware
// we used to install body parser but now it's a built in middleware
// Function of express. It parses incoming JSONpayload
// app.use(express.json({extended:false}));
app.use(express.json({ extended: false }));

// Test Routs
// app.get("/", (req,res)=>res.send("Hello Aruna !!!"));
// app.post("/", (req,res)=>res.send(`Hello ${req.body.name} `));
// app.get("/hello/:name", (req.res)=>res.send(`Hello ${req.params.name}`))

app.get('/api/articles/:name', async (req, res) => {
  try {
    const articleName = req.params.name;
    const db = client.db('mernblog');
    const articlesinfo = db
      .collection('articles')
      .findOne({ name: articleName });
    res.status(200).json(articlesinfo);
    client.close();
  } catch (error) {
    res.status(500).json({ message: 'Error connecting to database', error });
  }
});

app.post('/api/articles/:name/add-comments', (req, res) => {
  const { username, text } = req.body;
  const articleName = req.params.name;
  const db = client.db('mernblog');
  const articlesinfo = db
    .collection('articles')
    .updateOne({ name: articleName }, { $push: { comments: { username, text } } });
  res.status(200).send(articlesinfo);
});

app.post('/', (req, res) => res.send(`Hello ${req.body.name}`));
app.get('/hello/:name', (req, res) => res.send(`Hello ${req.params.name}`));

connectDB();

app.listen(PORT, () => console.log(`Server is running at port ${PORT}`));