Hologram v0.7.0: Milestone release for Elixir-to-JavaScript porting initiative (opens in new tab)

Thank you! The Elixir -> JS compiler is currently coupled with the framework - it's a custom thing, not a separate dependency.

Re the Gleam comparison: I don't know Gleam's implementation in detail so someone correct me if I'm wrong, but as I understand it - Gleam compiles to fairly readable JS with a minimal prelude, and deliberately treats the two targets as having different concurrency semantics. It doesn't try to replicate BEAM processes or OTP in JavaScript, instead using JS's native promise-based async. The upside is zero runtime overhead and clean JS interop.

Hologram takes the opposite approach - we're iteratively reimplementing the Erlang runtime in the browser, with the goal of having full semantic parity eventually. The tradeoff is a heavier runtime, but the benefit is that the same Elixir code can run on both server and client with consistent behavior.

I may be wrong but I believe the elixir->js compiler is currently built into the framework but it could potentially be separated in the future.

Gleam is different in that JS is a first-class target and built into Gleam's compiler, while Hologram is a standalone project.

Really appreciate it! Would love for you to give it another go - a lot has improved since then. If you run into any issues or have ideas for how things could be better, don't hesitate to reach out. Happy to help!

Oh yeah, I remember! We'll get there :) Hope you'll give Hologram another spin sometime soon!

Two big reasons: bundle size - few hundred KB uncompressed vs multiple MB already compressed with WASM. And the DOM lives in the JS world - WASM can't touch it directly and has to cross the JS bridge with serialization overhead every time.

On top of that, since the browser platform has different characteristics, you can surgically drop down to native JS functions instead of compiling and bundling everything. For example, things like Unicode code point databases are already built into the browser - no need to ship them in your bundle when you can just call into the native APIs. The compiled output is also readable which helps with debugging.

For web apps generally JS is the better target IMO - you want the smallest possible bundle and the app reacting as quickly as possible on load.

For serious apps it's impossible to escape reading Erlang or Erlang documentation. Many functions and libraries simply aren't available for Elixir or are partial (see `opentelemetry_*` family as an example). Deep debugging is almost exclusively done with Erlang functions.

I'd even say that the more serious/critical application becomes the more weight shifts toward Erlang. Personally I'd go with Erlang-first, but only because I've accumulated thousands paper cuts from Elixir.

For starters Elixir has much more palatable syntax, though.

It depends on what you're doing. I've been in Elixir web dev for about 7 years and never really needed to write or understand Erlang, outside of my work on Hologram. That said, Erlang is always there under the surface - it "leaks" into Elixir in places if you look at the stdlib, and understanding it gives you a better mental model of the whole platform. I'd say you don't need it on a daily basis for most Elixir work, but the runtime and OTP are incredible pieces of engineering, and getting to know Erlang better will only make you stronger in this ecosystem.

It's very easy to call Erlang from Elixir,

    value = :erlang.function(a, b, c)

So with that in mind, you can just learn Elixir, use Erlang where you need it for some libraries. Elixir is IMO much nicer to learn, write and use. I think it is worth learning a bit about the underlying systems but I've never felt like I should have put in 10 erlang-only projects before writing larger elixir stuff.

Both! Right now the focus is on enabling rich UIs with pure Elixir running in the browser. But eventually Hologram could be able to act as an Erlang node in the cluster as well.

Not currently, but expanding to Erlang is definitely possible down the road. I've actually been considering adding an Erlang compiler since some Erlang functions that the Elixir standard library depends on could be compiled automatically instead of being ported by hand.