---
title: Build for web
parent: Build ORT
nav_order: 4
---

# Build ONNX Runtime for Web
{: .no_toc }

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)

## Contents
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* TOC placeholder
{:toc}

## Build ONNX Runtime for WebAssembly

### Prerequisites

- Checkout the source tree:
  ```
  git clone --recursive https://github.com/Microsoft/onnxruntime
  cd onnxruntime
  ```
- [Install](https://cmake.org/download/) cmake-3.18 or higher.

- [Install](https://nodejs.org/) Node.js (14.0+)

  - (Optional) Use nvm ([Windows](https://github.com/coreybutler/nvm-windows) / [Mac/Linux](https://github.com/creationix/nvm)) to install Node.js

- Python (2.7 or 3.6+): https://www.python.org/downloads/
  - python should be added to the PATH environment variable

### Build Instructions

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

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

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

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

# The following command build release.
./build.sh --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](../tutorials/mobile/model-conversion.html).

### FAQ

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)

### Prerequisites

- [Install](https://nodejs.org/) Node.js (14.0+)

  - (Optional) Use nvm ([Windows](https://github.com/coreybutler/nvm-windows)/[Mac/Linux](https://github.com/creationix/nvm)) to install Node.js

- 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](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.

   - Build WebAssembly artifacts.

     1. Build ONNX Runtime WebAssembly

        Follow [instructions above](#build-onnx-runtime-for-webassembly) 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
   ```