5. Reusable Patterns for a DRY Code Base | Mastering Web Application Development with Express

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Mastering Web Application Development with Express

By : Alexandru Vladutu

3.7 (3)

Mastering Web Application Development with Express

3.7 (3)

By: Alexandru Vladutu

Overview of this book

If you are a Node.js developer who wants to take your Express skills to the next level and develop high performing, reliable web applications using best practices, this book is ideal for you. The only prerequisite is knowledge of Node.js.

Preface

Preface

What this book covers

What you need for this book

Who this book is for

Conventions

Reader feedback

Customer support

Free Chapter

1. Diving into Express

1. Diving into Express

The best parts of Express

Comparing Express with other frameworks

Use cases

Express into the wild

The application structure

Summary

2. Component Modularity Using Middleware

2. Component Modularity Using Middleware

Connecting middleware

The functionality of middleware

Creating configurable middleware

Environment-based loading of middleware

Express routes

Ordering of middleware

Handling errors with middleware

Mounting subapplications

Replicating the middleware system

Summary

3. Creating RESTful APIs

3. Creating RESTful APIs

An overview of REST

SmartNotes application requirements

Creating RESTful URLs of the application

Implementing the SmartNotes application

API versioning

API rate limiting

Throttling

Facilitating caching

Content negotiation

Summary

4. Leveraging the Power of Template Engines

4. Leveraging the Power of Template Engines

The different types of template engines

View helpers and application-level data

Sharing code between templates with partial views

DRY templates with layouts

Template engine consolidation with consolidate.js

View caching in production

Integrating a template engine with Express

Choosing a template engine

Summary

5. Reusable Patterns for a DRY Code Base

5. Reusable Patterns for a DRY Code Base

Creating the MovieApp sample application

Error checks and callback functions

Tiny modules for better control flow

Ensuring a single callback execution

Extending objects in a reusable way

A simple way to create custom errors

Summary

6. Error Handling

6. Error Handling

Runtime (operational) errors and human errors

Ways of delivering errors in the Node applications

Strings instead of errors as an antipattern

Improving stack traces

Handling uncaught exceptions

Logging errors

Creating a custom Express error handler

Richer errors with VError

Error handling in a practical application

Summary

7. Improving the Application's Performance

7. Improving the Application's Performance

Serving static resources with Express

Backend improvements

Summary

8. Monitoring Live Applications

8. Monitoring Live Applications

Logging

Simple tips for improving the application monitoring

Collecting metrics

Useful existing monitoring tools

Ensuring the application uptime

Summary

9. Debugging

9. Debugging

A better error-handling middleware

Using a debug flag

Debugging routes and middleware

Using the V8 debugger

Debugging memory leaks

Adding a REPL to our Express application

Removing debugging commands

Summary

10. Application Security

10. Application Security

Running Express applications on privileged ports

Cross-site request forgery protection

Cross-site scripting

HTTP security headers with Helmet

Handling file uploads

Session middleware parameters

Reauthenticating the user for sensitive operations

Summary

11. Testing and Improving Code Quality

11. Testing and Improving Code Quality

The importance of having automated tests

Testing toolbox

Creating and testing an Express file-sharing application

Running tests before committing in Git

Code coverage

Complexity analysis of our code

Code linting

Load testing

Client-side testing

Continuous Integration

Summary

Index

Index

Ensuring a single callback execution

We have used the after module to handle the parallel task, and this module does internal checks to ensure that the callback function has not already been executed. This check usually needs to be done because a function could be called with an error argument, triggering the callback function to be executed early. If the callback function has been run with an error parameter, we don't care about sending the final result after all the tasks have finished, because we expect the callback function to be executed only once.

Let's take a moment to reflect on the done callback function before using the after module to modify it:

var doneCalled = false;
var tasksCount = 2;
var done = function(err) {
  if (doneCalled) { return; }

  if (err) {
    doneCalled = true;
    return callback(err);
  };

  tasksCount--;

  if (tasksCount === 0) {
    movieInfo.trailers = trailers;
    movieInfo.cast = cast;

    callback(null, movieInfo);
  }
};

There is a doneCalled Boolean...

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