emsdk should be automatically installed at `<ORT_ROOT>/cmake/external/emsdk/emsdk`. If the folder structure does not exist, run the following commands in `<ORT_ROOT>/` to install git submodules:
```sh
git submodule sync --recursive
git submodule update --init --recursive
```
(If you are using Windows, you can skip this step) in `<ORT_ROOT>/cmake/external/emsdk/`, run the following commands to setup emsdk:
| `--enable_wasm_threads` | build with multi-thread support |
| `--enable_wasm_simd` | build with SIMD support |
A complete build for ONNX runtime WebAssembly artifacts will contain 4 ".wasm" files (ON/OFF configurations of the flags in the table above) with a few ".js" files.
The build command below should be run for each of the configurations.
> A: unittest requires C++ exceptions to work properly. However, for performance concern, we disabled exception catching in emscripten. So please specify `--skip_tests` in Release build.
Q: unittest fails on Debug build with debug info.
> A: building with debug info will generate very huge artifacts (>1GB for unittest) and failed to load in Node.js. So please specify `--skip_tests` in build with debug info.
Q: I have a C++ project for web scenario, which runs a ML model using ONNX Runtime and generates WebAssembly as an output. Does ONNX Runtime Web support a static WebAssembly library, so that my application can link with it and make all pre/post processors to be compiled together into WebAssembly?
> A: With `--build_wasm`, a build script generates `.wasm` and `.js` files for web scenarios and intermediate libraries are not linked properly with other C/C++ projects. When you build ONNX Runtime Web using `--build_wasm_static_lib` instead of `--build_wasm`, a build script generates a static library of ONNX Runtime Web named `libonnxruntime_webassembly.a` in output directory. To run a simple inferencing like an [unit test](https://github.com/microsoft/onnxruntime/blob/main/onnxruntime/test/wasm/test_inference.cc), what you need is three header files as follows and `libonnxruntime_webassembly.a`.
> One important note is that ONNX Runtime has dependencies on lots of 3rd party libraries such as protobuf, onnx, and others. You may need copy necessary header files to your project. You also take care of cases of library version conflicts or emsdk version conflicts between ONNX Runtime and your project.
You can either use the prebuilt artifacts or build it by yourself.
- Setup by script.
In `<ORT_ROOT>/js/web/`, run `npm run pull:wasm` to pull WebAssembly artifacts for latest master branch from CI pipeline.
- Download artifacts from pipeline manually.
you can download prebuilt WebAssembly artifacts from [Windows WebAssembly CI Pipeline](https://dev.azure.com/onnxruntime/onnxruntime/_build?definitionId=161&_a=summary). Select a build, download artifact "Release_wasm" and unzip. See instructions below to put files into destination folders.
