I am with difficulties in building the openCV.js in MAC OS

edit

I follow the steps in the tutorial at the openCV website and I have the following error:

bash-3.2# python platforms/js/build_js.py build_js
/Library/Frameworks/Python.framework/Versions/2.7/Resources/Python.app/Contents/MacOS/Python: can't open file 'platforms/js/build_js.py': [Errno 2] No such file or directory
bash-3.2# cd opencv/
bash-3.2# cd opencv-3.3.1/
bash-3.2# python platforms/js/build_js.py build_js
Args: Namespace(build_dir='build_js', build_doc=False, build_test=False, build_wasm=False, clean_build_dir=False, config_only=False, emscripten_dir='/Users/ruimfjesus/Applications/emsdk-portable/emscripten/1.37.22', enable_exception=False, opencv_dir='/Users/ruimfjesus/Applications/opencv/opencv-3.3.1', skip_config=False)
Check dir /Users/ruimfjesus/Applications/opencv/opencv-3.3.1/build_js (create: True, clean: False)
Check dir /Users/ruimfjesus/Applications/opencv/opencv-3.3.1 (create: False, clean: False)
Check dir /Users/ruimfjesus/Applications/emsdk-portable/emscripten/1.37.22 (create: False, clean: False)
Detected OpenCV version: 3.3.1
Detected emcc version: 1.37.22
=====
===== Config OpenCV.js build for asm.js
=====
Executing: ['cmake', '-DCMAKE_BUILD_TYPE=Release', "-DCMAKE_TOOLCHAIN_FILE='/Users/ruimfjesus/Applications/emsdk-portable/emscripten/1.37.22/cmake/Modules/Platform/Emscripten.cmake'", "-DCPU_BASELINE=''", "-DCPU_DISPATCH=''", '-DCV_TRACE=OFF', '-DBUILD_SHARED_LIBS=OFF', '-DWITH_1394=OFF', '-DWITH_VTK=OFF', '-DWITH_CUDA=OFF', '-DWITH_CUFFT=OFF', '-DWITH_CUBLAS=OFF', '-DWITH_NVCUVID=OFF', '-DWITH_EIGEN=OFF', '-DWITH_FFMPEG=OFF', '-DWITH_GSTREAMER=OFF', '-DWITH_GTK=OFF', '-DWITH_GTK_2_X=OFF', '-DWITH_IPP=OFF', '-DWITH_JASPER=OFF', '-DWITH_JPEG=OFF', '-DWITH_WEBP=OFF', '-DWITH_OPENEXR=OFF', '-DWITH_OPENGL=OFF', '-DWITH_OPENVX=OFF', '-DWITH_OPENNI=OFF', '-DWITH_OPENNI2=OFF', '-DWITH_PNG=OFF', '-DWITH_TBB=OFF', '-DWITH_PTHREADS_PF=OFF', '-DWITH_TIFF=OFF', '-DWITH_V4L=OFF', '-DWITH_OPENCL=OFF', '-DWITH_OPENCL_SVM=OFF', '-DWITH_OPENCLAMDFFT=OFF', '-DWITH_OPENCLAMDBLAS=OFF', '-DWITH_MATLAB=OFF', '-DWITH_GPHOTO2=OFF', '-DWITH_LAPACK=OFF', '-DWITH_ITT=OFF', '-DBUILD_ZLIB=ON', '-DBUILD_opencv_apps=OFF', '-DBUILD_opencv_calib3d=OFF', '-DBUILD_opencv_dnn=OFF', '-DBUILD_opencv_features2d=OFF', '-DBUILD_opencv_flann=OFF', '-DBUILD_opencv_ml=OFF', '-DBUILD_opencv_photo=OFF', '-DBUILD_opencv_imgcodecs=OFF', '-DBUILD_opencv_shape=OFF', '-DBUILD_opencv_videoio=OFF', '-DBUILD_opencv_videostab=OFF', '-DBUILD_opencv_highgui=OFF', '-DBUILD_opencv_superres=OFF', '-DBUILD_opencv_stitching=OFF', '-DBUILD_opencv_java=OFF', '-DBUILD_opencv_js=ON', '-DBUILD_opencv_python2=OFF', '-DBUILD_opencv_python3=OFF', '-DBUILD_EXAMPLES=OFF', '-DBUILD_PACKAGE=OFF', '-DBUILD_TESTS=OFF', '-DBUILD_PERF_TESTS=OFF', '-DBUILD_DOCS=OFF', '/Users/ruimfjesus/Applications/opencv/opencv-3.3.1']
Traceback (most recent call last):
  File "platforms/js/build_js.py", line 239, in <module>
    builder.config()
  File "platforms/js/build_js.py", line 179, in config
    execute(cmd)
  File "platforms/js/build_js.py", line 21, in execute
    raise Fail("Execution failed: %d / %s" % (e.errno, e.strerror))
__main__.Fail: Execution failed: 13 / Permission denied