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Getting started with Node.js
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getting-started.md

"How do I get started with Node?" is a commonly heard question in #Node.js. This gist is an attempt to compile some of the answers to that question.

And if this list didn't quite answer your questions, I'm available for tutoring and code review! A donation is also welcome :)

Javascript refresher

Especially if you normally use a different language, or you only use Javascript occasionally, it's easy to misunderstand some of the aspects of the language.

These links will help you refresh your knowledge of JS, and make sure that you understand the OOP model correctly.

  • A whirlwind tour of the language: http://learnxinyminutes.com/docs/javascript/
  • Javascript does automatic typecasting ("type conversion") in some cases. This shows how various values cast to a boolean, and this shows how null and undefined relate to each other.
  • In Javascript, braces are optional for single-line statements - however, you should always use them. This gist demonstrates why.
  • Asynchronous execution in Javascript is normally implemented using CPS. This stands for "continuation-passing style", and this shows an example of how that works.
  • However, in practice, you shouldn't use that, and you should use Promises instead. Whereas it is very easy to mess up CPS code, that is not an issue with Promises - error handling is much more reliable, for example. This guide should give you a decent introduction.
  • A callback should be either consistently synchronous, or consistently asynchronous. You don't really have to worry about this when you're using Promises (as they ensure that this is consistent), but this article still has a good explanation of the reasons for this. A simpler example can be found here.
  • Javascript does not have classes, and constructor functions are a bad idea. This short article will help you understand the prototypical OOP model that Javascript uses. This gist shows a brief example of what the this variable refers to. Often you don't need inheritance at all - this gist shows an example of creating an object in the simplest possible way.
  • In Javascript, closures are everywhere, by default. This gist shows an example.

The Node.js platform

Node.js is not a language. Rather, it's a "runtime" that lets you run Javascript without a browser. It comes with some basic additions such as a TCP library - or rather, in Node.js-speak, a "TCP module" - that you need to write server applications.

  • The easiest way to install Node.js on Linux and OS X, is to use nvm. The instructions for that can be found here. Make sure you create a default alias (as explained in the documentation), if you want it to work like a 'normal' installation.
  • If you are using Windows: You can download an installer from the Node.js website. You should consider using a different operating system, though - Windows is generally rather poorly suited for software development outside of .NET. Things will be a lot easier if you use Linux or OS X.
  • The package manager you'll use for Node.js, is called NPM. While it's very simple to use, it's not particularly well-documented. This article will give you an introduction to it. Don't hesitate to add dependencies, even small ones! Node.js and NPM are specifically designed to make this possible without running into issues.
  • The module system is very simple. The Node.js documentation explains this further.
  • MongoDB is commonly recommended and used with Node.js. It is, however, extremely poorly designed - and you shouldn't use it. This article goes into more detail about why you shouldn't use it. If you're not sure what to use, use PostgreSQL.
  • The rest of the documentation for all the modules included with Node.js, can be found here.

Setting up your environment

  • To be able to install "native addons" (compiled C++ modules), you need to take some additional steps. If you are on Linux or OS X, you likely already have everything you need - however, on Windows you'll have to install a few additional pieces of software. The instructions for all of these platforms can be found here. Do not skip this step. Installing pure-Javascript modules is not always a viable solution, especially where it concerns cryptography-related modules such as scrypt or bcrypt.
  • If you're running into issues on Windows, try these instructions from Microsoft.

Functional programming

Javascript has part of its roots in functional programming languages, which means that you can use some of those concepts in your own projects. They can be greatly beneficial to the readability and maintainability of your code.

  • This article gives an introduction to map, filter and reduce - three functional programming operations that help a lot in writing maintainable and predictable code.
  • This gist shows an example of using those with Bluebird, the Promises library that I recommended in the Promises Reading Guide.
  • This slide deck demonstrates currying in Javascript, another functional programming technique - think of them as "partially executed functions".

Module patterns

To build "configurable" modules, you can use a pattern known as "parametric modules". This gist shows an example of that. This is another example.

A commonly used pattern is the EventEmitter - this is exactly what it sounds like; an object that emits events. It's a very simple abstraction, but helps greatly in writing loosely coupled code. This gist illustrates the object, and the full documentation can be found here.

Code architecture

The 'design' of your codebase matters a lot. Certain approaches for solving a problem work better than other approaches, and each approach has its own set of benefits and drawbacks. Picking the right approach is important - it will save you hours (or days!) of time down the line, when you are maintaining your code.

I'm still in the process of writing more about this, but so far, I've already written an article that explains the difference between monolithic and modular code and why it matters. You can read it here.

Express

If you want to build a website or web application, you'll probably find Express to be a good framework to start with. As a framework, it is very small. It only provides you with the basic necessities - everything else is a plugin.

If this sounds complicated, don't worry - things almost always work "out of the box". Simply follow the README for whichever "middleware" (Express plugin) you want to add.

To get started with Express, simply follow the below articles. Whatever you do, don't use the Express Generator - it generates confusing and bloated code. Just start from scratch and follow the guides!

Some more odds and ends regarding about Express:

Some examples:

Combining Express and Promises:

Some common Express middleware that you might want to use:

Coming from other languages or platforms

  • If you are used to PHP or similar: Contrary to PHP, Node.js does not use a CGI-like model (ie. "one pageload is one script"). Instead, it is a persistent process - your code is the webserver, and it handles many incoming requests at the same time, for as long as the process keeps running. This means you can have persistent state - this gist shows an example of that.
  • If you are used to synchronous platforms: This gist illustrates the differences between a (synchronous) PHP script and an (asynchronous) Node.js application.

Security

Note that this advice isn't necessarily complete. It answers some of the most common questions, but your project might have special requirements or caveats. When in doubt, you can always ask in the #Node.js channel!

Also, keep in mind the golden rule of security: humans suck at repetition, regardless of their level of competence. If a mistake can be made, then it will be made. Design your systems such that they are hard to use incorrectly.

  • Sessions: Use something that implements session cookies. If you're using Express, express-session will take care of this for you. Whatever you do, don't use JWT for sessions, even if many blog posts recommend it - it will cause security problems. This article goes into more detail.
  • Password hashing: Use scrypt. This wrapper module will make it easier to use.
  • CSRF protection: You need this if you are building a website. Use csurf.
  • XSS: Every good templater will escape output by default. Only use templaters that do this (such as Jade or Nunjucks)! If you need to explicitly escape things, you should consider it insecure - it's too easy to forget to do this, and is practically guaranteed to result in vulnerabilities.
  • SQL injection: Always use parameterized queries. When using MySQL, use the node-mysql2 module instead of the node-mysql module - the latter doesn't use real parameterized queries. Ideally, use something like Knex, which will also prevent many other issues, and make your queries much more readable and maintainable.
  • Random numbers: Generating unpredictable random numbers is a lot harder than it seems. Math.random() will generate numbers that seem random, but are actually quite predictable by an attacker. If you need truly unpredictable random numbers, use something like the random-number-csprng module instead. Don't try to implement it yourself.
  • Cryptography: Follow the suggestions in this gist. Whatever you do, do not use the crypto module directly, unless you really have no other choice. Never use pure-Javascript reimplementations - always use bindings to the original implementation, where possible (in the form of native addons).
  • Vulnerability advisories: The Node Security Project keeps track of known vulnerabilities in Node.js modules. Services like VersionEye will e-mail you, if your project uses a module that is found vulnerable.

Useful modules:

This is an incomplete list, and I'll probably be adding stuff to it in the future.

Deployment

  • Don't run Node.js as root, ever! If you want to expose your service at a privileged port (eg. port 80), and you probably do, then you can use authbind to accomplish that safely.

Distribution

  • Your project is ready for release! But... you should still pick a license. This article will give you a very basic introduction to copyright, and the different kind of (common) licenses you can use.

Scalability

Scalability is a result of your application architecture, not the technologies you pick. Be wary of anything that claims to be "scalable" - it's much more important to write loosely coupled code with small components, so that you can split out responsibilities across multiple processes and servers.

Optimization

The first rule of optimization is: do not optimize.

The correct order of concerns is security first, then maintainability/readability, and then performance. Optimizing performance is something that you shouldn't care about, until you have hard metrics showing you that it is needed. If you can't show a performance problem in numbers, it doesn't exist; while it is easy to optimize readable code, it's much harder to make optimized core more readable.

There is one exception to this rule: never use any methods that end with Sync - these are blocking, synchronous methods, and will block your event loop (ie. your entire application) until they have completed. They may look convenient, but they are not worth the performance penalty.

Now let's say that you are having performance issues. Here are some articles and videos to learn more about how optimization and profiling works in Node.js / V8 - they are going to be fairly in-depth, so you may want to hold off on reading these until you've gotten some practice with Node.js:

These are some modules that you may find useful for profiling your application:

  • node-inspector: Based on Chrome Developer Tools, this tool gives you many features, including CPU and heap profiling. Also useful for debugging in general.
  • heapdump: On-demand heap dumps, for later analysis. Usable from application code in production, so very useful for making a heap dump the moment your application goes over a certain heap size.
  • memwatch-next: Provides memory leak detection, and heap diffing.

Writing C++ addons

You'll usually want to avoid this - C++ is not a memory-safe language, so it's much safer to just write your code in Javascript. V8 is rather well-optimized, so in most cases, performance isn't a problem either. That said, sometimes - eg. when writing bindings to something else - you just have to write a native module.

These are some resources on that:

Writing Rust addons

Neon is a new project that lets you write memory-safe compiled extensions for Node.js, using Rust. It's still pretty new, but quite promising - an introduction can be found here.

Odds and ends

Some miscellaneous code snippets and examples, that I haven't written a section or article for yet.

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