This way is easier as no extra but emcc required.

Simply following Step1 part of

https://github.com/treeform/nim_emscripten_tutorial

A more detailed version than the one above

https://github.com/bitnom/nim-to-wasm-guide

And you’ve get Nim running in Browser other than as JS (I’d mention Nim natively supports compiling to JS)

Export Symbols

emcc’s commandline options(in fact will to linker):

• -s EXPORT_ALL=1
• -s EXPORT_FUNCTIONS=_f1,... → export f1 (NOTE the beginning underscore) (bc. emcc mangles exported symbols. ref https://emscripten.org/docs/porting/connecting_cpp_and_javascript/Interacting-with-code.html#call-compiled-c-c-code-directly-from-javascript)
• I’ve found (as in 2025), util to gen export_name attribute also works for emcc
• using C macro EMSCRIPTEN_KEEPALIVE from <emscripten.h> (I tried but Nim compiler report errors, so I prefer method #3…)

Call Exported Function in JS