C++ WebAssembly in Node: instance.sum is not a function

I am learning with webassembly but I can not run basic simple app. I tried many possibilities, and none of them is working. My last aproach is this.

I am coding on Windows 10 so I installed emsdk from github.

git clone https://github.com/emscripten-core/emsdk.git
emsdk install latest
emsdk activate latest
emsdk_env.bat

I programmed this simple C++ code:

extern "C" {
    int sum(int a, int b) {
        return a + b;
    }
}

I compiled my source code like this:

em++ cpp-sources/Sum/sum.cpp -o sum/sum.js -s MODULARIZE

In javscript Node, I have this function:

public getSum(){
    const factory = require(__dirname + "/sum/sum.js");
    factory().then((instance) => {
        const sum = instance.sum as CallableFunction;
        console.log(sum(5, 6));
    });
}

After all my tries, it is still saying:

TypeError: sum is not a function

I also tried different approaches of calling wasm in Node. For example this one:

public getSum(){
    const fs = require('fs');
    const wasmBuffer = fs.readFileSync(__dirname + "/sum/sum.wasm");
    WebAssembly.instantiate(wasmBuffer).then(wasmModule => {
        const sum = wasmModule.instance.exports.sum as CallableFunction;
        const result = sum(5, 6);
        console.log(result);
    });
}

Result is same.

I have also another problem, that I can not include <emscripten.h> library in my C++ code.

Thank you for any ideas.

EDIT: I tried to compile C++ code to wasm with this:

em++ --no-entry cpp-sources/Sum/sum.cpp -o sum/sum.wasm  -s LINKABLE=1 -s EXPORT_ALL=1 -O2

Now when I run my typescript Node code, it has not error I mentioned before but new one:

[TypeError: WebAssembly.instantiate(): Imports argument must be present and must be an object]

I tried to update code as this:

public async getSum(){
    const binary = readFileSync(__dirname + "/sum/sum.wasm");
    const wasm = await WebAssembly.compile(binary);

    const importObject = {
        env: {
            memory: new WebAssembly.Memory({initial:10,maximum:10})
        }
    };

    WebAssembly.instantiate(wasm, importObject).then(instance => {
        const sum = instance.exports._sum as CallableFunction;
        const result = sum(5, 6);
        console.log(result);
    });
}

Now it has this error:

WebAssembly.instantiate(wasm, importObject).then(instance => {
                    ^
TypeError: WebAssembly.instantiate(): Import #257 module="wasi_snapshot_preview1" error: module is not an object or function
    at CalculatorService.<anonymous>