This article surveys 10 libraries that I have found to be tremendously useful while developing back-end node.js services. They mostly address generic tasks that you will come across again and again: support for configuration, logging, processing command-line arguments, code coverage, asynchronous control flow, unit testing and more. While the focus is mostly on supporting back-end services, some of these libraries can equally well be used for front-end JavaScript development. I picked these 10 libraries based purely on personal experience and am documenting them in the hope they will prove useful to others.

The libraries are discussed in decreasing order of the number of Github stars they had at the time of writing this article, so more popular libraries are discussed first, and the lesser-known gems are discussed near the bottom. Don’t let this ranking trick you into thinking that this is a “top 10” article: I’m not comparing these libraries against one another.

Enough intro, let’s get started!

Next week I will be speaking at jsconf.be in lovely Bruges, Belgium. It’s the second edition of the local Belgian JavaScript community gathering and it’s promising to be quite an interesting program with talks on some of the usual suspects: React, Angular, Meteor, node and some less usual suspects, like the Cody CMS, a content-management system written 100% in JS. Perhaps unsurprisingly given recent events, I will be speaking about ECMAScript 6, which is nearing completion (at the time of writing, TC39 itself has signed off on the spec, but it is pending formal approval from ECMA). This is quite a historical moment. As Allen Wirfs-Brock, the editor of the ES6 spec put in the foreword of the new spec:

My student Mattias De Wael, with guidance from Stefan Marr and myself, recently published a study on how the Java Fork/Join framework is being used in practice by developers. From the abstract:

The Fork/Join framework […] is part of the standard Java platform since version 7. Fork/Join is a high-level parallel programming model advocated to make parallelizing recursive divide-and-conquer algorithms particularly easy. While, in theory, Fork/Join is a simple and effective technique to expose parallelism in applications, it has not been investigated before whether and how the technique is applied in practice. We therefore performed an empirical study on a corpus of 120 open source Java projects that use the framework for roughly 362 different tasks. On the one hand, we confirm the frequent use of four best-practice patterns (from Doug Lea’s book) – Sequential Cutoff, Linked Subtasks, Leaf Tasks, and avoiding unnecessary forking – in actual projects. On the other hand, we also discovered three recurring anti-patterns that potentially limit parallel performance: sub-optimal use of Java collections when splitting tasks into subtasks as well as when merging the results of subtasks, and finally the inappropriate sharing of resources between tasks.

To me, the most interesting outcome was the observation that the Fork/Join API could benefit from the Java Collections API being extended with collections that can be efficiently split and merged. Often, developers choose suboptimal data structures, or suboptimal methods on existing data structures to do recursive splits/merges. Although perhaps that isn’t even necessary, as it turns out Java 8 Streams effectively cover typical use cases of Fork/Join such as parallel maps and reduces, without the developer having to manually split and merge the collection anymore. The paper has been accepted at PPPJ 2014. The original submission can be accessed here.

We recently published a new article on AmbientTalk, an actor language I co-designed with a focus on developing mobile applications for ad hoc wireless networks. The main novelty of the article is what we believe to be the first formal account of the communicating event loops model, which is the concurrency model underlying the family of actor languages upon which AmbientTalk is based. Interestingly, this model is also closest to the concurrency model you get in JavaScript, if you think of a WebWorker as an actor. The article gives a comprehensive overview of AmbientTalk’s roots, the language itself, and introduces a “featherweight AmbientTalk” calculus with an operational semantics. We use it to establish data race freedom (actors have isolated memory) and deadlock freedom (assuming all event loop turns are finite, all asynchronous messages sent between actors will eventually be processed). The article is published in the journal “Computer Languages, Systems & Structures”. A preprint copy of the paper is available here. Quoting the abstract:

The rise of mobile computing platforms has given rise to a new class of applications: mobile applications that interact with peer applications running on neighbouring phones. Developing such applications is challenging because of problems inherent to concurrent and distributed programming, and because of problems inherent to mobile networks, such as the fact that wireless network connectivity is often intermittent, and the lack of centralized infrastructure to coordinate the peers. We present AmbientTalk, a distributed programming language designed specifically to develop mobile peer-to-peer applications. AmbientTalk aims to make it easy to develop mobile applications that are resilient to network failures by design. We describe the language’s concurrency and distribution model in detail, as it lies at the heart of AmbientTalk’s support for responsive, resilient application development. The model is based on communicating event loops, itself a descendant of the actor model. We contribute a small-step operational semantics for this model and use it to establish data race and deadlock freedom.

As of this month, I’m working for Alcatel-Lucent Bell Labs in Antwerp, Belgium. I will be doing distributed systems research with a focus on programmability and programming models. I’m still active part-time at the VUB Software Languages Lab.