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Try it out!

There's two ways to try out the current state of the wasm port without building anything yourself.

  1. An instance of the Web REPL hosted at
  2. Using the iodide IDE plugin (see to get started).

Both use a pre-built version. Please note that this is an extremely early alpha and many things are likely (and known) to be broken.

Julia on WASM - Setup instructions

This repo contains various experiments for setting up julia on wasm. It's intended for collaboration and issue tracking before things are working sufficiently to switch to the appropriate upstream repo: There's three scripts in this repo:

  • which will setup all the directories
  • which will build two copies of julia (one natively for cross compiling the system image, one for wasm)
  • which will rebuild just the wasm parts and dump it into the website/ directory which is a hacked up copy of

To get started


  1. nodejs
  2. gcc-multilib and g++-multilib

Emscripten SDK

First install the emscripten SDK

# Install emsdk
git clone
cd emsdk
./emsdk install emscripten-main-64bit binaryen-main-64bit
./emsdk activate emscripten-main-64bit binaryen-main-64bit

Upstream LLVM

Then build and install upstream LLVM

# Install upstream LLVM
git clone
mkdir llvm-build
cd llvm-build
cmake -G Ninja -DLLVM_ENABLE_PROJECTS="clang;lld" -DCMAKE_BUILD_TYPE=Release ../llvm-project/llvm

Setup environment

  1. Add LLVM_ROOT = '<PATH_TO_LLVM_HERE>/llvm-build/bin' to $HOME/.emscripten
  2. Add llvm-build/bin to $PATH

Bootstrapped build

Finally, you're ready to build julia for wasm

# Do this once
# this command may fail at the very end of the build process, that's normal

This command may fail at the very end with an error like the following:

    JULIA build-native/usr/lib/julia/sys-o.a
syntax: incomplete: premature end of inputErrorException("")
ERROR: LoadError: syntax: incomplete: premature end of input
 [1] top-level scope at /root/julia-wasm/julia/contrib/generate_precompile.jl:7

This is expected (we're using a 32bit linux build, but telling it it's wasm to generate a compatible system image, so things are a bit confused). Afterwards, build the wasm build using:

 # Do this after you change something on the wasm side

Afterwards you may set up a webserver using:

emrun --no_browser --port 8888 website/repl.htm &

At the moment Firefox Nightly seems to have the most complete wasm support and seems to be the fastest, so I'd recommend trying that. After starting the server above, just navigate to localhost:8888/repl.htm

Enable WASM GC support integration (Firefox Nightly)

In about:config enable javascript.options.wasm_gc

Enable WASM Reference Types (Chrome Canary)

google-chrome-unstable  --jsflags="--experimental-wasm-anyref"