[I am using ubuntu 18.04 vm (prefered) for compiling]

Set up the WebAssembly compiler (emscripten) using https://webassembly.org/getting-started/developers-guide/

$ git clone https://github.com/juj/emsdk.git
$ cd emsdk
$ ./emsdk install --build=Release sdk-incoming-64bit binaryen-master-64bit
$ ./emsdk activate --build=Release sdk-incoming-64bit binaryen-master-64bit

start the terminal

admin@admin-Virtual-Machine:~/$ cd emsdk                 
admin@admin-Virtual-Machine:~/emsdk$ source ./emsdk_env.sh --build=Release

Setting environment variables:
EMSDK = /home/admin/emsdk

admin@admin-Virtual-Machine:~/emsdk$ cd ..
admin@admin-Virtual-Machine:~/emsdk$ mkdir example
admin@admin-Virtual-Machine:~/$ cd example [this directory has the c/c++ code to be compiled into WebAssembly]
admin@admin-Virtual-Machine:~/example$ gedit test.c [take test.c from this repo]
admin@admin-Virtual-Machine:~/example$ ls
test.c

admin@admin-Virtual-Machine:~/example$ emcc test.c -o test.js -s WASM=1 -s NO_EXIT_RUNTIME=1 -s EXTRA_EXPORTED_RUNTIME_METHODS='["ccall"]'

input: test.c

output: test.js, test.wasm

admin@admin-Virtual-Machine:~/example$ ls

test.c 
test.js [generated]
test.wasm [generated]

Using WASM files in Javascript
-------------------------------

admin@admin-Virtual-Machine:~/example$ gedit index.html [take index.html from this repo]

Refer https://developer.mozilla.org/en-US/docs/WebAssembly/C_to_wasm for after installation steps.

Just run index.html and see the result. [firefox, edge prefered to run locally. chrome CORS prevents local system file access]

• Go to https://wasdk.github.io/WasmFiddle/
• Type the C function

int square(a) { 
  return a*a;
}

• Build

• Download wasm

• create an html file 'square_usage.html'

<script>
WebAssembly.instantiateStreaming(fetch('square.wasm'))
      .then(obj => {
         console.log(obj.instance.exports.square(5));
      });
</script>

• Run with a local web server (Required due to fetch API-CORS)

For Refer: https://stackoverflow.com/a/58256067/12167785

• Run

node --experimental-modules --experimental-wasm-modules simplemath.mjs