Add possibility for disabling inlining `wasm` in `opencv.js`

doc/js_tutorials/js_setup/js_setup/js_setup.markdown

@@ -83,6 +83,9 @@ Building OpenCV.js from Source
     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.
+    By default everything is bundled into one JavaScript file by `base64` encoding the WebAssembly code. For production
+    builds you can add `--disable_single_file` which will reduce total size by writing the WebAssembly code
+    to a dedicated `.wasm` file which the generated JavaScript file will automatically load.
 
     For example, to build wasm version in `build_wasm` directory:
     @code{.bash}

modules/js/CMakeLists.txt

@@ -70,7 +70,7 @@ if(COMPILE_FLAGS)
 endif()
 
 set(EMSCRIPTEN_LINK_FLAGS "${EMSCRIPTEN_LINK_FLAGS} --memory-init-file 0 -s TOTAL_MEMORY=128MB -s WASM_MEM_MAX=1GB -s ALLOW_MEMORY_GROWTH=1")
-set(EMSCRIPTEN_LINK_FLAGS "${EMSCRIPTEN_LINK_FLAGS} -s MODULARIZE=1 -s SINGLE_FILE=1")
+set(EMSCRIPTEN_LINK_FLAGS "${EMSCRIPTEN_LINK_FLAGS} -s MODULARIZE=1")
 set(EMSCRIPTEN_LINK_FLAGS "${EMSCRIPTEN_LINK_FLAGS} -s EXPORT_NAME=\"'cv'\" -s DEMANGLE_SUPPORT=1")
 set(EMSCRIPTEN_LINK_FLAGS "${EMSCRIPTEN_LINK_FLAGS} -s FORCE_FILESYSTEM=1 --use-preload-plugins --bind --post-js ${JS_HELPER} ${COMPILE_FLAGS}")
 set_target_properties(${the_module} PROPERTIES LINK_FLAGS "${EMSCRIPTEN_LINK_FLAGS}")

platforms/js/build_js.py

@@ -180,6 +180,8 @@ class Builder:
             flags += "-s WASM=1 "
         elif self.options.disable_wasm:
             flags += "-s WASM=0 "
+        if not self.options.disable_single_file:
+            flags += "-s SINGLE_FILE=1 "
         if self.options.threads:
             flags += "-s USE_PTHREADS=1 -s PTHREAD_POOL_SIZE=4 "
         else:
@@ -233,6 +235,7 @@ if __name__ == "__main__":
     parser.add_argument('--emscripten_dir', default=emscripten_dir, help="Path to Emscripten to use for build (deprecated in favor of 'emcmake' launcher)")
     parser.add_argument('--build_wasm', action="store_true", help="Build OpenCV.js in WebAssembly format")
     parser.add_argument('--disable_wasm', action="store_true", help="Build OpenCV.js in Asm.js format")
+    parser.add_argument('--disable_single_file', action="store_true", help="Do not merge JavaScript and WebAssembly into one single file")
     parser.add_argument('--threads', action="store_true", help="Build OpenCV.js with threads optimization")
     parser.add_argument('--simd', action="store_true", help="Build OpenCV.js with SIMD optimization")
     parser.add_argument('--build_test', action="store_true", help="Build tests")