In Ductape has to save a Js Callback function passed a parameter to a C function

C++ calls the JS function, JsFunc(), passsing a C-function, MyCFunc(), as a parameter. JsFunc() calls MyCFunc() passsing a JS callback function as parameter.

How do I save in MyCFunc() the JS callback function parameter so that I can call it later from somewhere else in C++?

main.cpp

#include <duktape/src/duktape.h>
#include <cassert>

duk_ret_t MyCFunc(duk_context* ctx) {
    assert(duk_is_function(ctx, -1) );
    (void) duk_require_function(ctx, -1);

    // 1.- How to save the callback function parameter
    //     so that it can be used later on, say in main()?
    return 0; // nothing returned
}

int main() {
    duk_context* ctx = duk_create_heap_default();
    assert(ctx != nullptr);

    if (duk_peval_file(ctx, "../../src/jscallback_forum/test.js") != 0) {
        printf("Error: %s\n", duk_safe_to_string(ctx, -1));
        exit(1);
    }
    duk_pop(ctx);  /* ignore result */

    duk_push_global_object(ctx);
    duk_bool_t isSuccess = duk_get_prop_string(ctx, -1 , "JsFunc");
    assert(isSuccess != false);

    // pass  MyCFunc as parameter to JsFunc
    duk_push_c_function(ctx, &MyCFunc, 1); // MyCFunc expects Js callback

    if (duk_pcall(ctx, 1) != 0) { // JsFunc call failed
        printf("Error: %s\n", duk_safe_to_string(ctx, -1));
    }

    duk_pop(ctx);  /* pop duk_pcall result/error */
    duk_pop(ctx);  /* pop duk_push_global_object */

// 2. How do I retrieve the JS callback function 
    //    saved in MyCFunc() and run it?

    duk_destroy_heap(ctx);

    return 0;
}

test.js

function JsFunc(cfunc) {
    print("Entering testCFunc" );

    cfunc(function () {
        print("In lambda function()");
    });

    print("Exiting testCFunc");

}