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Building Xeact components with esbuild and Nix

Read time in minutes: 21

Xeact has succeeded in its goal of intergalactic domination of the attention space of frontend developers. Not only has it been the catalyst towards my true understanding of front-end development, it is the most popular frontend femtoframework as signified by this handy graph:

hero image blog/2023/xeact/star-history-202342

However, my deployment process for Xeact components relies on the deno bundle command, which is being deprecated:

Warning "deno bundle" is deprecated and will be removed in the future.
Use alternative bundlers like "deno_emit", "esbuild" or "rollup" instead.

I have always hated the process of deploying JavaScript code to the internet. npm creates massive balls of mud that are so logistically annoying to tease out into actual real files that your browser can load. The tooling around building JavaScript projects into real files has historically been a trash fire of philosophical complexity and has been the sole reason that I have avoided digging too deep into how frontend development works.

Cadey is coffee
<Cadey> Really though, it really sucks that the way that Node.js development is so different than what browsers actually support. I know that browsers getting import map support can help with this, but it would be nice if that wasn't a problem at all.

I understand why the Deno team is getting rid of the deno bundle command (and at some level, based on what I've learned it's actually quite amazing that I have gotten this all working in browsers to begin with), but just dumping the horrors of esbuild onto unsuspecting people is logistically frustrating. Especially with how much you need to hack at all of this.

Cadey is coffee
<Cadey> I really don't want all of this to sound negative and hateful. But really, from the perspective of someone used to doing distribution packaging with languages that normally compile to single binaries, the Node ecosystem is a huge pain in the ass. At one time Debian tried to enforce a policy of every separate dependency being compiled to its own unversioned package. All this fell apart when they realized that different node packages will depend on the unspoken behavior of separate transitive dependencies. This has lead to them giving up and shipping vendored node_modules folders.

Can you see why I like Rust as a distribution packager? I don't have to deal with any problems other than making sure the binary builds and I can slap it in the package. It is so easy in comparison.

However, I really don't want my builds to randomly start breaking at some uncertain point in the future when I upgrade Deno. So, I got bored and then decided to convert my entire build system over to esbuild. Here is the entire stack and how I got it working for my builds.

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Deno and esbuild

Aoi is wut
<Aoi> So if esbuild is the thing you are supposed to be using, why would you not want to use it? Are you not using NPM or something?

You're right my foxy friend, I'm not using NPM or even node.js at all. I'm using Deno, which is an alternative JavaScript/TypeScript runtime that is written in Rust and makes dependency management so much easier. One of the main ways that it makes dependency management easier is by having you pull packages from URLs running normal static file servers instead of having to put everything into NPM and then hope that NPM doesn't go down.

Cadey is coffee
<Cadey> Yes, yes, this does mean that you need to hope that the other fileservers hosting your dependencies don't go down. However when Nix and the like is brought into the situation later in the article, this becomes less of a problem.

When you install a package with Deno, it downloads all of the relevant JavaScript and TypeScript files to somewhere on disk and stores them based on their origin server and SHA256 checksum. This is very unlike what NPM does. As a comparison, here's what the file tree for NPM installing Xeact:

`-- @xeserv
    `-- xeact
        |-- LICENSE
        |-- default.nix
        |-- jsx-runtime.js
        |-- package.json
        |-- shell.nix
        |-- site
        |   |-- gruvbox.css
        |   |-- index.html
        |   `-- index.js
        |-- types
        |   |-- jsx-runtime.d.ts
        |   `-- xeact.d.ts
        |-- xeact.js
        `-- xeact.ts

And here's what Deno's local file tree looks like:

`-- https
        |-- 15c8dd50d4aede83901b65e305f1eca8dd42955da363aca395949ce932023443
        |-- 15c8dd50d4aede83901b65e305f1eca8dd42955da363aca395949ce932023443.metadata.json
        |-- 6291a9332210dc73f237e710bb70d6aab7f8cd66ea82cb680ed70f83374b34a3
        `-- 6291a9332210dc73f237e710bb70d6aab7f8cd66ea82cb680ed70f83374b34a3.metadata.json

You can see how this would give existing tooling a lot of trouble.

Luckily, esbuild has support for plugins. These let you override behavior like how esbuild looks for dependencies. There is a Deno plugin for esbuild, but it is chronically under-documented. Here is how I got it working.

First, I added esbuild and the deno plugin to my import map:

  "imports": {
    "@esbuild": "",
    "@esbuild/deno": "",

Mara is hacker
<Mara> You can use any name you want for this, but @esbuild and @esbuild/deno looks cool.

Then write a file named build.ts with the following things in it:

import * as esbuild from "@esbuild";
import { denoPlugin } from "@esbuild/deno";

const result = await{
  plugins: [denoPlugin({
    importMapURL: new URL("./import_map.json", import.meta.url),
  entryPoints: Deno.args,
  outdir: Deno.env.get("WRITE_TO")
    ? Deno.env.get("WRITE_TO")
    : "../../static/xeact",
  bundle: true,
  splitting: true,
  format: "esm",
  minifyWhitespace: !!Deno.env.get("MINIFY"),
  inject: ["xeact"],
  jsxFactory: "h",


Mara is hacker
<Mara> Don't forget the esbuild.stop call. If you don't, the script will hang infinitely. This was "fun" to discover on the fly.

This will do the following:

  • Configure esbuild to read from our Deno dependencies with the import map
  • Sets all of the command line arguments to be the build inputs, so you can call it with deno run -A build.ts **/*.tsx and get it to magically build all of the files in ./components
  • Sets the output paths and if the output should be minified based on environment variables (used in the Nix build)

This builds everything correctly, and puts each component in its own .js file where my site expects to serve it. This will be important later.


Now comes the fun part, making all of this work deterministically in Nix so that I can inevitably forget how all of this works because it all happens behind the scenes. When I build my site's frontend with Nix, I use my fork of deno2nix to automate the process of setting up a local copy of all the dependencies my website depends on.

The deno2nix internal.mkDepsLink function allows you to take a deno.lock file and turn that into a folder in the Nix store. This does all of the hard parts of making a Deno build work in Nix. It converts the deno.lock file into the folder structure that Deno created.

There's only one small problem: I pull dependencies from, which sometimes has you include files with @ (at-signs) in their paths. For example:

This would be pulled into the Nix store as /nix/store/if9bjhar81hhm7rqrlb4rfs65k2rwnp0-xeact@0.70.0, which doesn't work because of this error:

error: store path 'if9bjhar81hhm7rqrlb4rfs65k2rwnp0-xeact@0.70.0' contains illegal character '@'

There's two ways of fixing this:

  • Fix deno2nix so that it strips @ from the basename (final path component) of URLs
  • Take advantage of how works to require from the exact files instead of the parent level re-exports

When you read from, you get a file that re-exports the actual NPM package like this for

/* - @xeserv/xeact@0.70.0 */
export * from "";
export { default } from "";

This means that you can just change the imports to the path instead of making it import the top-level /@xeserv/xeact@0.70.0, and this will work because the basename is xeact.mjs, not xeact@0.70.0. This will let it fit into the Nix store.

After changing over all the import paths to pull from exact files instead of the top-level packages, deno2nix worked with the old build flow. Now all that is left is running the esbuild wrapper. After noodling for a while, I came up with this derivation:

frontend = pkgs.stdenv.mkDerivation rec {
    pname = "xesite-frontend";
    inherit (bin) version;
    dontUnpack = true;
    src = ./src/frontend;
    buildInputs = with pkgs; [ deno jq nodePackages.uglify-js ];
    ESBUILD_BINARY_PATH = "${pkgs.esbuild}/bin/esbuild";

    buildPhase = ''
        export DENO_DIR="$(pwd)/.deno2nix"
        mkdir -p $DENO_DIR
        ln -s "${pkgs.deno2nix.internal.mkDepsLink ./src/frontend/deno.lock}" $(deno info --json | jq -r .modulesCache)
        export MINIFY=yes

        mkdir -p dist
        export WRITE_TO=$(pwd)/dist

        pushd $(pwd)
        cd $src
        deno run -A ./build.ts **/*.tsx

    installPhase = ''
        mkdir -p $out/static/xeact
        cp -vrf dist/* $out/static/xeact

This uses the internal.mkDepsLink function to create everything we need, minifies the output, writes it all to a folder named dist and finally plunks everything into $out/static/xeact, such as with MastodonShareButton.js.

It worked, and I was so relieved when it did.


Now that I had the ability to build all of my dynamic components, I had to take a moment to design something I've wanted to make for a while, the Xeact Component Model. At a high level, Xeact is built for stateless components. These components are functionally identical as React components: functions that take in properties and turn them into HTML nodes.

Mara is hacker
<Mara> In more computer science terminology, we can call these monomorphisms. Monomorphisms are functions that take one argument and produce one result, such as (x) -> x + 1 in JavaScript. State really muddies up the waters, but let's not think about that for now.

Here's an example Xeact component, the one that handles the "No fun allowed" button for talk pages:

import { c } from "xeact";

const onclick = () => {
  Array.from(c("xeblog-slides-fluff")).forEach((el) =>

export default function NoFunAllowed() {
  const button = (
      onclick={() => onclick()}
      No fun allowed
  return button;

This creates a function called NoFunAllowed that shows a button that says "No fun allowed". When a user clicks on it, it toggles the "hidden" class on every element with the CSS class xeblog-slides-fluff. When I write talks I usually use my slides as tools to help me visually explain what's going on. Combined with a healthy dose of surrealism, this means that some people may find the written forms of my talks jarring due to all of the tweet-length paragraphs combined with memes and absurdism, such as what is quite possibly my favorite slide I've ever made:

Cadey is coffee
<Cadey> At some level, I really get that people don't like this. It's slightly frustrating to me as an artist to know that so many people don't really see the value in the art that I pour so much effort into, but I get it. Humor is hard. Abstract humor is harder. Abstract humor about abstractions stapled on top of abstractions is something that many people will miss. I enjoy using absurdist/surrealist humor to really communicate the inherent surrealism of our profession to people. For many people it's just fundamentally a swing and a miss. I'll live.

It was a simple copy/paste/useState job to migrate over all of the other dynamic components. Then came wiring it up on the server side.

The server

Let's go back to what Xeact components really are: functions that take attributes and return HTML nodes. When I write the HTML for my server-side components, I really am writing things like this in the markdown:

<xeblog-conv name="Mimi" mood="coffee">As a large language model, I
can serve to provide some example text. I don't know what "Hipster
Ipsum" is. But the Lorem Ipsum text...</xeblog-conv>

This gets expanded into what you see in the document with lol_html:

Mimi is coffee
<Mimi> As a large language model, I can serve to provide some example text. I don't know what "Hipster Ipsum" is. But the Lorem Ipsum text...

So at some level I need to do the following things to support Xeact components:

  • Create a HTML wrapper that imports the component and places it into the HTML tree with a unique UUID
  • Have some kind of <noscript> tag to warn people that they need to have JavaScript enabled
  • A little hacky JavaScript that imports the component and executes it with JSON passed from Rust

I think I have most of this with my xeact_component template. It creates a unique ID (UUIDv4), serializes data from Rust into JSON so that it can be used as inputs to Xeact components, and then slaps the results of the component function into the element tree.

I used this basic process to port over my other dynamic components such as the video player:

Cadey is enby
<Cadey> I have plans to write a review about Returnal when I finish it. It's an absolute masterpiece.

My hope is that this will make it easier for me to maintain and expand on the other components on my website. Eventually I want to make a HTML tag that is like <xeact-component xeact_filename="Thing" foo="bar">, and then have all the rest of the stack do the right thing, but that will take a bit more creativity than I can muster right now.

I am really happy that this all works, not only will this make it easier for me to run my website, extending it in the future should be even easier.

Cadey is coffee
<Cadey> This is starting to break my "no structural JavaScript" rule that I put on myself, but realistically this is the direction the entire ecosystem is going anyways. I don't like that this will reduce compatibility with other browsers like LibWeb from SerenityOS, but I need to have access to fancy toys to be able to experiment.

I would love to reuse this logic in waifud eventually. Its admin panel is also vulnerable to the same eventual breakage, and I suspect that I will inevitably reuse this build logic there too. Not to mention the Xeact component model and useState allowing me to simplify a lot of the logic there too.

This article was posted on M04 08 2023. Facts and circumstances may have changed since publication. Please contact me before jumping to conclusions if something seems wrong or unclear.

Tags: nix xeact esbuild frontend

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The art for Mara was drawn by Selicre.

The art for Cadey was drawn by ArtZora Studios.

Some of the art for Aoi was drawn by @Sandra_Thomas01.