Setting up the swagger
Swagger UI can be set up for both the front end & backend as well. Since this article is about the Swagger with Node.js. I will be setting up the the swagger in Node.js express app only. you can explore the other options here
 
In your api.js
    //Swagger Configuration  
    const swaggerOptions = {  
        swaggerDefinition: {  
            info: {  
                title:'Employee API',  
                version:'1.0.0'  
            }  
        },  
        apis:['api.js'],  
    }  
    const swaggerDocs = swaggerJSDoc(swaggerOptions);  
    app.use('/api-docs',swaggerUI.serve,swaggerUI.setup(swaggerDocs));  
       
After integrating the swagger setup lets define the swagger endpoint with description and response codes in a particular format so that we can able to access those API's inside the swagger after running in the browser
 
Add Swagger Before Each End Point
    /**
     * @swagger
     * /Employees:
     *   get:
     *     description: Get all Employee
     *     responses:  
     *       200:
     *         description: Success  
     *   
     */  
    app.get('/Employees',(req,res)=>{  
        res.send([  
            {  
                id:1, Name:'Jk'  
            },  
            {  
                id:2,Name:'Jay'  
            }  
        ])  
    });  

For the demo purpose, I have added four API's (Get, Post, Put, Delete) added the swagger setup for the remaining endpoints as well
 
Final api.js
    const express = require('express');  
    const swaggerJSDoc = require('swagger-jsdoc');  
    const swaggerUI = require('swagger-ui-express');  
      
    const app = express();  
      
    app.listen(5000,()=>console.log("listening on 5000"));  
      
    //Swagger Configuration  
    const swaggerOptions = {  
        swaggerDefinition: {  
            info: {  
                title:'Employee API',  
                version:'1.0.0'  
            }  
        },  
        apis:['api.js'],  
    }  
    const swaggerDocs = swaggerJSDoc(swaggerOptions);  
    app.use('/api-docs',swaggerUI.serve,swaggerUI.setup(swaggerDocs));  
       
    /**
     * @swagger
     * /Employees:
     *   get:
     *     description: Get all Employee
     *     responses:  
     *       200:
     *         description: Success  
     *   
     */  
    app.get('/Employees',(req,res)=>{  
        res.send([  
            {  
                id:1, Name:'Jk'  
            },  
            {  
                id:2,Name:'Jay'  
            }  
        ])  
    });  
      
    /**
     * @swagger
     * /Employees:
     *   post:
     *     description: Create an Employee
     *     parameters:
     *     - name: EmployeeName
     *       description: Create an new employee
     *       in: formData
     *       required: true
     *       type: String
     *     responses:  
     *       201:
     *         description: Created  
     *   
     */  
     app.post('/Employees',(req,res)=>{  
       res.status(201).send();  
    });  
    /**
     * @swagger
     * /Employees:
     *   put:
     *     description: Create an Employee
     *     parameters:
     *     - name: EmployeeName
     *       description: Create an new employee
     *       in: formData
     *       required: true
     *       type: String
     *     responses:  
     *       201:
     *         description: Created  
     *   
     */  
     app.put('/Employees',(req,res)=>{  
        res.status(201).send();  
     });  
     /**
     * @swagger
     * /Employees:
     *   delete:
     *     description: Create an Employee
     *     parameters:
     *     - name: EmployeeName
     *       description: Create an new employee
     *       in: formData
     *       required: true
     *       type: String
     *     responses:  
     *       201:
     *         description: Created  
     *   
     */  
      app.delete('/Employees',(req,res)=>{  
        res.status(201).send();  
     });  

Run the URL in the browser
Now you can do the npm start in the terminal to your app and it will navigate to the browser we have to add the /api-docs at the end of the URL so that i will navigate to the swagger which we have configured and you will see the Swagger UI based on your generated swagger.json.
 
Terminal

Swagger

Testing the API with Swagger