git clone https://github.com/juj/emsdk.git
cd emsdk
git pull
./emsdk install latest
./emsdk activate latest
source ./emsdk_env.sh
$ cd opencv
# Build asm.js version
$ python ./platforms/js/build_js.py build_js
# Build wasm version
$ python ./platforms/js/build_js.py build_wasm --build_wasm