facing an issue while connecting nodejs app(container a) and sql server (container b)

web docker file

FROM node:14
WORKDIR /app 
COPY package*.json ./ 


RUN npm install 
COPY . . 
EXPOSE 3000 
CMD ["npm", "start"

db docker file

FROM mcr.microsoft.com/mssql/server:2019-latest

EXPOSE 1433

docker compose file

version: "3.8"
services:
  db:
    build: ./db
    environment:
      SA_PASSWORD: mahe@123
      ACCEPT_EULA: Y
      MSSQL_PID: Developer
    ports:
      - "1433:1433"
    restart: always

  web:
    build: ./web
    environment:
      DB_CONNECTION_STRING: Server=localhost;Database=Bitespeed;User Id=sa;Password=mahe@123;
    ports:
      - "3000:3000"
    depends_on:
      - db
    restart: on-failure

dbconfig.js file

const config = {
  user: 'sa',
  password: 'mahe@123',
  server: 'localhost',
  database: 'Bitespeed',

  options: {
    enableArithAort: true,
    trustServerCertificate:true
  },
  port: 1433
}

module.exports = config; 

server.js file

const express = require('express')
const app = express()
const bodyParser = require('body-parser')
const sql = require('mssql');
const config = require("./dbconfig")
require('dotenv').config()

const port = process.env.PORT

app.use(bodyParser.urlencoded({extended: true}))
app.use(bodyParser.json())

const mainRouter = require('./router')
app.use('/api',mainRouter)

function connectWithRetry(){
    return sql.connect(config,(err) => {
 
         if (err) {
             console.log(`Connection to DB failed, retry in 5s `,err.message)
             sql.close()
             setTimeout(connectWithRetry(), 5000);
         }
         else {
             console.log('Connected to SQL Server successfully');
         }
     }); 
 }

 connectWithRetry()

app.listen(port , ()=>{
    console.log("app is listening on port " + port)
})

can any plase help me what is the error. and i am getting the following error

enter image description here

and my db is running fine..enter image description here

can any one help me with this..

i am expecting my node app will connect to the sql server.

In your case, localhost will point to the container itself (web). You can specify the docker-compose alias of the database service (db) instead in your config:

const config = {
  ...
  server: 'db',
  ...
  port: 1433
}

Since you are also setting an environment variable DB_CONNECTION_STRING in your docker-compose.myml which seems to overwrite your settings, you probably also need to change the "localhost" in that environment variable:

web:
  build: ./web
  environment:
    DB_CONNECTION_STRING: Server=db;Database=Bitespeed;User Id=sa;Password=mahe@123;`