- Execute arbitrary code
- Call the next middleware function using the **```next()```** command
- Make changes to the ```req``` and ```res``` objects
- End the request-response cycle

const express = require('express')
const app = express()
const router = express.Router()

// application level middleware
app.use((req, res, next) => {
  // There is no specified mount path. It will execute every time this app receives a request.
  console.log("My first middleware function!")
  res.send("Method type: " + req.method)
})

// router level middleware
router.use('/:id', (req, res, next) => {
  // Printing the type of request for the specified id 
  console.log(req.method)
  next()
})

// error handling middleware
app.use((err, req, res, next) => {
  // Sending an error message as a response to a 400 error
  res.status(400).send(err.message)
})

app.listen(3000)

import React from 'react';
import { shallow, configure } from 'enzyme';
import Adapter from 'enzyme-adapter-react-16';

configure({ adapter: new Adapter() });

import HelloWorld from './app';

var TestResult = function() {
    this.succeeded = false;
    this.reason = "";
    this.input = "";
    this.expected_output = "";
    this.actual_output = "";
}

export const executeTests = function() {

  var results = [];

  result = new TestResult();
  result.input = 'HelloWorld Component';
  result.expected_output = "span containing text 'Hello World'"

  let wrapper = shallow(<HelloWorld />);

  // Call your Challenge function here.

  let type = wrapper.type();
  let testSuccessful = true;
  let failureReason;

  if (type !== 'span') {
    testSuccessful = false;
    failureReason = "You need to render exactly one span HTML element";
  } else if (wrapper.props().children != "Hello World") {
     testSuccessful = false;
     failureReason = "You have rendered wrong message in your span element";
  }

  result.actual_output = wrapper.html();

  if (testSuccessful) {
    result.succeeded = true;
    result.reason = "Succeeded"
  } else {
    result.succeeded = false;
    result.reason = failureReason;
  }

  results.push(result);

  return results;
}


React

Dart

GoJS React

Typescript React

Vue.js

expressjs.tar.gz

What is Express.js middleware?

Express.js middleware functions add extra functionality to handle arbitrary code, modify requests/responses, and manage errors in the request-response cycle.

What is Express.js middleware?

Overview

Syntax

Explanation