npm init -y
npm install express swagger-ui-express
npm install --save-dev swagger-autogen

create app.js file

const express = require('express');
const app = express();
const port = process.env.port || 3000;

/*Swagger configurations start*/
const swaggerUi = require('swagger-ui-express');
const swaggerDocument = require('./swagger.json');

app.use('/api-docs', swaggerUi.serve, swaggerUi.setup(swaggerDocument));
/*Swagger configurations end*/

app.get('/', (req, res) => {
    res.send('Nice to meet you!');
});

app.get('/products', (req, res) => {
    const products = [
        {
            id: 1,
            name: "hammer",
        },
        {
            id: 2,
            name: "screwdriver",
        },
        {
            id: 3,
            name: "wrench",
        },
    ];

    res.json(products);
});

app.listen(port, () => {
    console.log(`app is running on http://localhost:${port}`);
});

create swagger.js file

const swaggerAutogen = require('swagger-autogen')();
const path = require('path');

const doc = {
  info: {
    title: 'SM Tool API'
  }
};

const outputFile = path.join(__dirname, './swagger.json');
const endpointFiles = ['./app.js'];

swaggerAutogen(outputFile, endpointFiles, doc);

generate swagger.json file

node swagger.js

run app

node app.js

check results on http://localhost:3000/api-docs