Installing Emscripten

Emscripten is an LLVM-to-JavaScript compiler. We will use Emscripten to build OpenCV.js.

To Install Emscripten, follow instructions of Emscripten SDK.

For example:

./emsdk update
./emsdk install latest
./emsdk activate latest

Note: To compile to WebAssembly, you need to install and activate Binaryen with the emsdk command. Please refer to Developer's Guide for more details.

After install, ensure the EMSCRIPTEN environment is setup correctly.

For example:

source ./emsdk_env.sh

echo ${EMSCRIPTEN}

Obtaining OpenCV Source Code

You can use the latest stable OpenCV version or you can grab the latest snapshot from our Git repository.

Launch Git client and clone OpenCV repository.

For example:

git clone https://github.com/opencv/opencv.git

To build opencv.js, execute python script <opencv_src_dir>/platforms/js/build_js.py <build_dir>.

For example, to build in build_js directory:
cd opencv
python ./platforms/js/build_js.py build_js
Note
It requires python and cmake installed in your development environment.
The build script builds asm.js version by default. To build WebAssembly version, append --build_wasm switch.

For example, to build wasm version in build_wasm directory:
python ./platforms/js/build_js.py build_wasm --build_wasm
[optional] To build documents, append --build_doc option.

For example:
python ./platforms/js/build_js.py build_js --build_doc
Note
It requires doxygen installed in your development environment.
[optional] To build tests, append --build_test option.

For example:
python ./platforms/js/build_js.py build_js --build_test
To run tests, launch a local web server in <build_dir>/bin folder. For example, node http-server which serves on localhost:8080.

Navigate the web browser to http://localhost:8080/tests.html, which runs the unit tests automatically.

You can also run tests using Node.js.

For example:
cd bin
npm install
node tests.js
Note
It requires node installed in your development environment.