JavaScript Containers

Ryan Dahl

The majority of server programs are Linux programs. They consist of a file system, some executable files, maybe some shared libraries, they probably interface with system software like systemd or nsswitch.

Docker popularized the use of Linux containers; OS level virtualization that provides a wonderful mechanism for distributing server software. Each container image is a dependency-free ready-to-run software package.

Because server software often depends on many system resources and configuration, deploying it has been challenging in the past. Linux containers solved that.

A similar hermetic environment can be found in browser JavaScript, albeit at a higher level of abstraction. Zack Bloom at Cloudflare motivated us back in 2018 to wonder if JavaScript itself can provide a new type of self-contained server container.

The more we can remove unnecessary abstractions, the closer we can get to the concept of "The Network Is the Computer". Cloudflare Workers is essentially an implementation of this concept in the Cloudflare network. Deno Deploy is a new implementation of this idea (on the GCP network).

In this post I’ll describe how I think about JavaScript Containers and speculate about how this technology will unfold over the next couple years.

The Universal Scripting Language

Technology is difficult to predict, but certainly the World Wide Web will be here in 10 years. Every passing day sees more and more human infrastructure tied together via web apps - the web is eating the world. If you believe the web will be here in 10 years, then certainly the standards that make up the web - HTTP, HTML, CSS, JavaScript - will be here. Thus I’m confident that JavaScript will continue to be developed and improved.

The web is the fundamental medium of human information. JavaScript is unlike other programming languages in that it is deeply tied into this infrastructure.

Scripting languages make a lot of sense for many server-side problems. Most of the code being written is not compute bound, rather it’s bound by productivity: the speed it can be written and the monetary cost of the developers. Scripting languages allow business logic to be written faster and cheaper. The scripting languages (Python, Ruby, Lua, Shell, Perl, Smalltalk, JavaScript) are pretty similar. There are differences in syntax and APIs, but there’s little else to contrast them with. Anyone who has spent time in Rust or C understands how scripting languages feel.

To summarize: scripting languages are useful, but they’re all pretty much the same, of them JavaScript is by far more wildly used and future proof. Thus it makes sense to think of JavaScript as the universal scripting language.

Shell : Executables :: JavaScript : WebAssembly

There is a new higher level container emerging for server software: the JavaScript sandbox itself.

This container isn’t meant to address the same breadth of problems that Linux containers target. Its emergence is a result of its simplicity. It minimizes the boilerplate for web service business logic. It shares concepts with the browser and reduces the concepts that the programmer needs to know. (Example: when writing a web service, very likely any systemd configuration is just unnecessary boilerplate.)

Every web engineer already knows JavaScript browser APIs. Because the JS container abstraction is built on the same browser APIs, the total amount of experience the engineer needs is reduced. The universality of Javascript reduces complexity.

Shell is the interpreted scripting language used to invoke Unix programs. It can do conditionals, loops, it has variables… but it is unfortunately limited and difficult to program. Real functionality is relegated to executables.

In this emerging server abstraction layer, JavaScript takes the place of Shell. It is quite a bit better suited to scripting than Bash or Zsh. Instead of invoking Linux executables, like shell does, the JavaScript sandbox can invoke Wasm. If you have some computational heavy lifting, like image resizing, it probably makes sense to use Wasm rather than writing it in JS. Just like you wouldn’t write image resizing code in bash, you’d spawn imagemagick.

The North Star

The future of scripting languages is browser JavaScript. The fundamental mistake of Node.js was diverging from the browser as new APIs were standardized, inventing too much. In 2010, we didn’t have ES modules, but once it was standardized it should have been brought into Node. The same can be said for promises, async/await, fetch, streams, and more. Antiquated non-standard bits like CommonJS require, package.json, node_modules, NPM, the global process object will ultimately either be standardized and added to the browser or supplanted by web-aligned replacements.

This higher level container is yet to be standardized. We don’t quite know how all this will pan out. For the moment Cloudflare Workers and Deno Deploy use the FetchEvent API:

addEventListener("fetch", (event) => {
  event.respondWith(new Response("Hello world"));

It might be that a better interface yet can be found.


JavaScript is the universal scripting language. Due to JavaScript’s universality a new container-like abstraction is emerging that simplifies servers.

I am not claiming that Linux containers are going away. That level of abstraction will always be useful. It’s just rather low-level for much of the “business logic” that people write. When you’re building a website things like systemd configuration are boilerplate.

Maybe the majority of “web services” can be simplified by thinking in terms of JavaScript containers, rather than Linux containers.

At Deno we are exploring these ideas; we’re trying to radically simplify the server abstraction. We’re hiring if this sounds interesting to you.

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