[Docs] Mention emnapi in documentation (#17515)

Author: toyobayashi

site/source/docs/porting/connecting_cpp_and_javascript/Interacting-with-code.rst

@@ -798,6 +798,16 @@ for defining the binding:
    of one tool over the other will usually be based on which is the most
    natural fit for the project and its build system.
 
+.. _interacting-with-code-emnapi:
+
+Binding C/C++ and JavaScript - Node-API
+===============================================================
+
+`Emnapi`_ is an unofficial `Node-API`_ implementation which can be used
+on Emscripten. If you would like to port existing Node-API addon to WebAssembly
+or compile the same binding code to both Node.js native addon and WebAssembly,
+you can give it a try. See `Emnapi documentation`_ for more details.
+
 .. _library.js: https://github.com/emscripten-core/emscripten/blob/main/src/library.js
 .. _test_js_libraries: https://github.com/emscripten-core/emscripten/blob/1.29.12/tests/test_core.py#L5043
 .. _src/deps_info.json: https://github.com/emscripten-core/emscripten/blob/main/src/deps_info.json
@@ -808,3 +818,6 @@ for defining the binding:
 .. _test/test_core.py: https://github.com/emscripten-core/emscripten/blob/1.29.12/tests/test_core.py#L4597
 .. _Box2D: https://github.com/kripken/box2d.js/#box2djs
 .. _Bullet: https://github.com/kripken/ammo.js/#ammojs
+.. _Emnapi: https://github.com/toyobayashi/emnapi
+.. _Node-API: https://nodejs.org/dist/latest/docs/api/n-api.html
+.. _Emnapi documentation: https://emnapi-docs.vercel.app/guide/getting-started.html