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Pratik Das
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error handling code
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‎nodejs/errorhandling/README.md‎

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# Examples for [Error Handling in Express](guide-to-error-handling-in-express)
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This repository contains the source code of the article's examples.

‎nodejs/errorhandling/js/index.js‎

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const express = require('express')
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const axios = require("axios")
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// const morgan = require('morgan')
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const app = express()
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const requestLogger = (request, response, next) => {
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console.log(`${request.method} url:: ${request.url}`);
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next()
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}
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app.use(express.static('images'))
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app.use(express.static('htmls'))
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app.use('/products', express.json({ limit: 100 }))
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// Error handling Middleware functions
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const errorLogger = (error, request, response, next) => {
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console.log( `error ${error.message}`)
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next(error) // calling next middleware
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}
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const errorResponder = (error, request, response, next) => {
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response.header("Content-Type", 'application/json')
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const status = error.status || 400
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response.status(status).send(error.message)
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}
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const invalidPathHandler = (request, response, next) => {
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response.status(400)
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response.send('invalid path')
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}
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// handle post request for path /products
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app.post('/products', (request, response) => {
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const products = []
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const name = request.body.name
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const brand = request.body.brand
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const category = request.body.category
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if(name == null){
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res.status(500).json({ message: "Mandatory field name is missing. " })
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}else{
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console.log(name + " " + brand)
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products.push({name: request.body.name, brand: request.body.brand, price: request.body.price})
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const productCreationResponse = {productID: "12345", result: "success"}
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response.json(productCreationResponse)
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}
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})
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app.get('/products', async (request, response, next)=>{
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try{
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const apiResponse = await axios.get("http://localhost:3001/products")
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const jsonResponse = apiResponse.data
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console.log("response "+jsonResponse)
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response.send(jsonResponse)
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}catch(error){
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next(error)
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}
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})
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app.get('/product', (request, response, next)=>{
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axios.get("http://localhost:3001/product")
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.then(response=>response.json)
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.then(jsonresponse=>response.send(jsonresponse))
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.catch(next)
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})
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app.get('/productswitherror', (request, response) => {
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let error = new Error(`processing error in request at ${request.url}`)
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error.statusCode = 400
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throw error
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})
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app.use(errorLogger)
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app.use(errorResponder)
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app.use(invalidPathHandler)
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const port = 3000
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app.listen(3000,
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() => console.log(`Server listening on port ${port}.`));
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‎nodejs/errorhandling/js/lambda.js‎

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console.log('Loading function');
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const validateRecord = (recordElement)=>{
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// record is considered valid if contains status field
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return recordElement.includes("status")
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}
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exports.handler = async (event, context) => {
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/* Process the list of records and transform them */
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const output = event.records.map((record)=>{
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const decodedData = Buffer.from(record.data, "base64").toString("utf-8")
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let isValidRecord = validateRecord(decodedData)
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if(isValidRecord){
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let parsedRecord = JSON.parse(decodedData)
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// read fields from parsed JSON for some more processing
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const outputRecord = `status::${parsedRecord.status}`
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return {
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recordId: record.recordId,
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result: 'Ok',
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// payload is encoded back to base64 before returning the result
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data: Buffer.from(outputRecord, "utf-8").toString("base64")
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}
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}else{
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return {
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recordId: record.recordId,
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result: 'dropped',
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data: record.data // payload is kept intact,
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}
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}
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})
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};

‎nodejs/errorhandling/js/server.js‎

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const express = require('express')
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// const morgan = require('morgan')
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const app = express()
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const port = 3001
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const products = [
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{name:"Television", price: 24.56, currency: "USG", brand: "samsung"},
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{name:"Washing Machine", price: 67.56, currency: "EUR", brand: "LG"}
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]
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app.get('/products', (request, response)=>{
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response.json(products)
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})
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app.listen(port,
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() => console.log(`Server listening on port ${port}.`))
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‎nodejs/errorhandling/package.json‎

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{
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"name": "storefront",
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"version": "1.0.0",
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"description": "",
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"main": "js/index.js",
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"scripts": {
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"test": "echo \"Error: no test specified\" && exit 1"
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},
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"keywords": [],
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"author": "",
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"license": "ISC",
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"dependencies": {
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"axios": "^0.26.1",
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"express": "^4.17.3",
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"node-fetch": "^3.2.2"
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},
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"devDependencies": {
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"@types/express": "^4.17.13",
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"@types/node": "^17.0.23",
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"ts-node": "^10.7.0",
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"typescript": "^4.6.3"
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}
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}

‎nodejs/errorhandling/ts/app.ts‎

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import express, { Request, Response, NextFunction } from 'express'
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import axios from 'axios'
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const app = express()
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const port:number = 3000
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interface Product {
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name: string
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price: number
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brand: string
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category?: string
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}
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interface ProductCreationResponse {
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productID: string
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result: string
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}
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class AppError extends Error{
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statusCode: number;
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constructor(statusCode: number, message: string) {
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super(message);
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Object.setPrototypeOf(this, new.target.prototype);
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this.name = Error.name;
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this.statusCode = statusCode;
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Error.captureStackTrace(this);
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}
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}
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const requestLogger = (request: Request, response: Response, next: NextFunction) => {
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console.log(`${request.method} url:: ${request.url}`);
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next()
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}
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app.use(express.static('images'))
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app.use(express.static('htmls'))
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app.use(requestLogger)
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app.use('/products', express.json({ limit: 100 }))
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// Error handling Middleware functions
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const errorLogger = (error: Error, request: Request, response: Response, next: NextFunction) => {
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console.log( `error ${error.message}`)
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next(error) // calling next middleware
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}
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const errorResponder = (error: AppError, request: Request, response: Response, next: NextFunction) => {
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response.header("Content-Type", 'application/json')
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const status = error.statusCode || 400
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response.status(status).send(error.message)
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}
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const invalidPathHandler = (request: Request, response: Response, next: NextFunction) => {
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response.status(400)
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response.send('invalid path')
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}
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// handle post request for path /products
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app.post('/products', (request: Request, response: Response) => {
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const products = []
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const name = request.body.name
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const brand = request.body.brand
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const category = request.body.category
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if(name == null){
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response.status(500).json({ message: "Mandatory field name is missing. " })
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}else{
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console.log(name + " " + brand)
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products.push({name: request.body.name, brand: request.body.brand, price: request.body.price})
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const productCreationResponse = {productID: "12345", result: "success"}
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response.json(productCreationResponse)
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}
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})
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app.get('/products', async (request: Request, response: Response, next: NextFunction)=>{
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try{
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const apiResponse = await axios.get("http://localhost:3001/products")
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const jsonResponse = apiResponse.data
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console.log("response "+jsonResponse)
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response.send(jsonResponse)
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}catch(error){
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next(error)
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}
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})
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app.get('/product', (request: Request, response: Response, next: NextFunction)=>{
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axios.get("http://localhost:3001/product")
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.then(jsonresponse=>response.send(jsonresponse))
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.catch(next)
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})
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app.get('/productswitherror', (request, response) => {
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let error:AppError = new AppError(400, `processing error in request at ${request.url}`)
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error.statusCode = 400
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throw error
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})
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app.get('/productswitherror', (request: Request, response: Response) => {
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let error: AppError = new AppError(400, `processing error in request at ${request.url}`)
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throw error
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})
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app.use(errorLogger)
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app.use(errorResponder)
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app.use(invalidPathHandler)
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app.listen(port, () => {
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console.log(`Server listening at port ${port}.`)
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})

‎nodejs/errorhandling/ts/server.ts‎

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import express, { Request, Response, NextFunction } from 'express'
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const app = express()
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const port:number = 3001
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interface Product {
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name: string
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price: number
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currency: string
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brand: string
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category?: string
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}
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const products: Product[] = [
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{name:"Television", price: 24.56, currency: "USG", brand: "samsung"},
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{name:"Washing Machine", price: 67.56, currency: "EUR", brand: "LG"}
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]
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app.get('/products', (request: Request, response: Response)=>{
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response.json(products)
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})
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app.listen(port,
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() => console.log(`Server listening on port ${port}.`))
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‎nodejs/errorhandling/tsconfig.json‎

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{
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"compilerOptions": {
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"module": "commonjs",
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"target": "es6",
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"rootDir": "./ts",
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"esModuleInterop": true
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}
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}

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