Dependency injection in Express - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import Express and create an app instance.

Express

const express = require('[1]');
const app = express();

Drag options to blanks, or click blank then click option'

Apath

Bhttp

Cfs

Dexpress

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'http' instead of 'express' to import Express.

Forgetting to require the module before using it.

The Express library is imported by requiring 'express'. This creates the Express module needed to create the app.

2fill in blank

medium

Complete the code to inject a dependency into a route handler using Express's request object.

Express

app.get('/greet', (req, res) => {
  const greeter = req.[1].greeter;
  res.send(greeter.greet());
});

Drag options to blanks, or click blank then click option'

Aparams

Bbody

Ccontainer

Dquery

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'req.body' which holds POST data, not dependencies.

Using 'req.params' or 'req.query' which hold URL parameters.

Dependency injection can be done by attaching dependencies to a custom property on the request object, often named 'container' or similar.

3fill in blank

hard

Fix the error in the middleware that injects a service into the request object.

Express

function injectService(req, res, next) {
  req.[1] = { greeter: { greet: () => 'Hello!' } };
  next();
}

Drag options to blanks, or click blank then click option'

Acontainer

Binject

Cservices

Dservice

Attempts:

3 left

💡 Hint

Common Mistakes

Using inconsistent property names causing undefined errors.

Not calling next() to pass control to the next middleware.

Using 'req.container' is a common pattern to hold injected dependencies in Express middleware.

4fill in blank

hard

Fill both blanks to create middleware that injects a logger service and use it in a route.

Express

function injectLogger(req, res, next) {
  req.[1] = { log: (msg) => console.log(msg) };
  next();
}

app.get('/log', (req, res) => {
  req.[2].log('Logging a message');
  res.send('Logged');
});

Drag options to blanks, or click blank then click option'

Acontainer

Bservices

Clogger

Dinject

Attempts:

3 left

💡 Hint

Common Mistakes

Using different property names in middleware and route causing undefined errors.

Forgetting to call next() in middleware.

Both middleware and route handler use 'req.container' to access injected services consistently.

5fill in blank

hard

Fill all three blanks to define a service, inject it via middleware, and use it in a route.

Express

const greeterService = {
  greet: () => '[1]'
};

function injectServices(req, res, next) {
  req.[2] = { greeter: greeterService };
  next();
}

app.get('/hello', (req, res) => {
  res.send(req.[3].greeter.greet());
});

Drag options to blanks, or click blank then click option'

AHello, friend!

Bcontainer

Dservices

Attempts:

3 left

💡 Hint

Common Mistakes

Using different property names for injection and access.

Returning the wrong greeting string.

The service returns a greeting string. Middleware injects it into 'req.container'. The route reads from 'req.container' to call the greet method.