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syrusakbary Merge pull request #173 from davidMcneil/172
Fix emscripten environment (#172)
Latest commit 7602071 Feb 16, 2019


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Wasmer is a Standalone JIT WebAssembly runtime, aiming to be fully compatible with Emscripten, Rust and Go.

Install Wasmer with:

curl https://get.wasmer.io -sSfL | sh

NEW : Now you can also embed Wasmer in your Rust application, check our example repo to see how to do it!


wasmer can execute both the standard binary format (.wasm) and the text format defined by the WebAssembly reference interpreter (.wat).

Once installed, you will be able to run any WebAssembly files (including Nginx, and Lua!):

# Run Lua
wasmer run examples/lua.wasm

# Run Nginx
wasmer run examples/nginx/nginx.wasm -- -p examples/nginx -c nginx.conf

Code Structure

Wasmer is structured into different directories:

  • src: code related to the wasmer excutable binary itself
  • lib: modularized libraries that Wasmer uses under the hood
  • examples: some useful examples to getting started with wasmer


Building wasmer requires rustup.

To build on Windows, download and run rustup-init.exe then follow the onscreen instructions.

To build on other systems, run:

curl https://sh.rustup.rs -sSf | sh

Other dependencies

Please select your operating system:


If you have homebrew installed:

brew install cmake

Or, in case you have ports:

sudo port install cmake

Debian-based Linuxes

sudo apt install cmake

Windows (MSVC)

Windows support is highly experimental. Only simple wasm programs may be run, and no syscalls are allowed. This means nginx and lua do not work on Windows. See this issue for ongoing Emscripten syscall polyfills for Windows.

  1. Install Python for Windows (https://www.python.org/downloads/release/python-2714/). The Windows x86-64 MSI installer is fine. You should change the installation to install the "Add python.exe to Path" feature.

  2. Install Git for Windows (https://git-scm.com/download/win). DO allow it to add git.exe to the PATH (default settings for the installer are fine).

  3. Install CMake (https://cmake.org/download/). Ensure CMake is in the PATH.


Wasmer is built with Cargo, the Rust package manager.

# checkout code
git clone https://github.com/wasmerio/wasmer.git
cd wasmer

# install tools
# make sure that `python` is accessible.
cargo install --path .


Thanks to spectests we can assure 100% compatibility with the WebAssembly spec test suite.

Tests can be run with:

make test

If you need to re-generate the Rust tests from the spectests you can run:

make spectests

You can also run integration tests with:

make integration-tests


Wasmer is an open project guided by strong principles, aiming to be modular, flexible and fast. It is open to the community to help set its direction.

Below are some of the goals (written with order) of this project:

  • It should be 100% compatible with the WebAssembly Spectest
  • It should be fast (partially achieved)
  • Support Emscripten calls (in the works)
  • Support Rust ABI calls
  • Support GO ABI calls


If you would like to know how Wasmer works under the hood, please visit our ARCHITECTURE document.