Error building openCV.js

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I am trying to build OpenCV.js following the steps in this tutorial.

The process fails with the following output:

make[3]: *** [3rdparty/lib/liblibprotobuf.a] Error 1
make[2]: *** [3rdparty/protobuf/CMakeFiles/libprotobuf.dir/all] Error 2
make[1]: *** [modules/js/CMakeFiles/opencv.js.dir/rule] Error 2
make: *** [opencv.js] Error 2
Traceback (most recent call last):
  File "./platforms/js/build_js.py", line 247, in <module>
    builder.build_opencvjs()
  File "./platforms/js/build_js.py", line 182, in build_opencvjs
    execute(["make", "-j", str(multiprocessing.cpu_count()), "opencv.js"])
  File "./platforms/js/build_js.py", line 19, in execute
    raise Fail("Child returned: %s" % retcode)
__main__.Fail: Child returned: 2

Does anybody know what this means or how it can be resolved?

I am on macOS High Sierra and my python version is 2.7.10.