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Build ONNX Runtime for Web

There are 2 steps to build ONNX Runtime Web:

  • build ONNX Runtime for WebAssembly
    • or skip and download a pre-built artifacts
  • build onnxruntime-web (NPM package)


Build ONNX Runtime for WebAssembly


  • Checkout the source tree:
    git clone --recursive
    cd onnxruntime
  • Install cmake-3.18 or higher.

  • Install Node.js (14.0+)

  • Python (2.7 or 3.6+):
    • python should be added to the PATH environment variable

Build Instructions

in <ORT_ROOT>/, run one of the following commands to build WebAssembly:

# In windows, use 'build' to replace './'

# The following command build debug.
./ --build_wasm

# The following command build debug with debug info.
./ --build_wasm --skip_tests --enable_wasm_debug_info

# The following command build release.
./ --config Release --build_wasm --skip_tests --disable_wasm_exception_catching --disable_rtti

ONNX Runtime WebAssembly can be built with or without multi-thread/SIMD support, specified by appending the following flags.

build flag usage
--enable_wasm_threads build with multi-thread support
--enable_wasm_simd build with SIMD support

To get all build artifacts of ONNX Runtime WebAssembly, it needs 4 times of build with the combinations of ON/OFF of the 2 flags. A full list of build artifacts are as below:

file name --enable_wasm_threads --enable_wasm_simd
ort-wasm.js X X
ort-wasm.wasm X X
ort-wasm-threaded.js O X
ort-wasm-threaded.wasm O X
ort-wasm-threaded.worker.js O X
ort-wasm-simd.wasm X O
ort-wasm-simd-threaded.wasm O O

Minimal Build Support

ONNX Runtime WebAssembly can be built with flag --minimal_build. This will generate smaller artifacts and also have a less runtime memory usage. An ORT format model is required. A detailed instruction will come soon. See also ONNX Model Conversion.


Q: unittest fails on Release build.

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.

Build onnxruntime-web (NPM package)


  • Install Node.js (14.0+)

  • Chrome or Edge browser for running tests.

Build Instructions

  1. Install NPM packages

    1. in <ORT_ROOT>/js/, run npm ci.
    2. in <ORT_ROOT>/js/common/, run npm ci.
    3. in <ORT_ROOT>/js/web/, run npm ci.
  2. Prepare ONNX Runtime WebAssembly artifacts.

    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. Select a build, download artifact “Release_wasm” and unzip. See instructions below to put files into destination folders.

    • Build WebAssembly artifacts.

      1. Build ONNX Runtime WebAssembly

        Follow instructions above for building ONNX Runtime WebAssembly.

      2. Copy following files from build output folder to <ORT_ROOT>/js/web/dist/ (create the folder if it does not exist):

        • ort-wasm.wasm
        • ort-wasm-threaded.wasm (build with flag ‘–enable_wasm_threads’)
        • ort-wasm-simd.wasm (build with flag ‘–enable_wasm_simd’)
        • ort-wasm-simd-threaded.wasm (build with flags ‘–enable_wasm_threads –enable_wasm_simd’)
      3. Copy following files from build output folder to <ORT_ROOT>/js/web/lib/wasm/binding/:

        • ort-wasm.js
        • ort-wasm-threaded.js (build with flag ‘–enable_wasm_threads’)
        • ort-wasm-threaded.worker.js (build with flag ‘–enable_wasm_threads’)
  3. Use following command in folder <ORT_ROOT>/js/web to build:

    npm run build