Q: Example of using JS callbacks about duktape HOT 11 OPEN

#define bindjs(n) duk_ret_t n (duk_context *J)
static long callbacks = 0;
bindjs (add_callback) {
	const char *str = duk_get_string(J , 0); // 0

	duk_push_global_stash(J);			// 1 push the global stash to store the function object.
	duk_push_number(J, callbacks);		// 2 key
	duk_dup(J, 0);						// 3 duplicate the function argument so we can use duk_put_prop*
	duk_put_prop(J, -3);				// store the function with given key.

	duk_pop(J);							// remove the stash object.

	callbacks++;
	return 0;
}
bindjs (specific_callback) {
	int n = duk_get_top(J);
	if (n == 1) {
		duk_push_global_stash(J); // 1 obj

		duk_dup(J, 0); // 2
		if (duk_get_prop(J, -2)) {
			if (duk_is_function(J, -1)) {
				duk_call(J, 0); // adapt with number of arguments.
				duk_pop(J); // remove return value
			} else printf("%s not a function\n", duk_get_string(J, -1));

			duk_dup(J, 0); // 2
			duk_del_prop(J, -2); // auto pops key from stack as well
		} else printf("%s not found\n", duk_to_string(J, 0));
		duk_pop(J);  // remember to pop, regardless of whether or not present
		
		duk_pop(J); // remove the stash object.
	}
	return 0;
}
bindjs (process_callbacks) {
	duk_push_global_stash(J); // 1 obj

	duk_enum(J, -1, DUK_ENUM_INCLUDE_NONENUMERABLE); // 2 enum
	
	while (duk_next(J, -1 /*enum_idx*/, 1 /*get_value*/)) { // 3 key 4 val
		if (duk_is_function(J, -1)) {
			duk_call(J, 0); // adapt with number of arguments.
			duk_pop(J); // remove return value
		}

		duk_del_prop(J, -3); // auto pops key from stack as well

	}

	duk_pop(J); // pop enum object
	
	duk_pop(J); // remove the stash object.

	print_duk_stack();
	return 0;
}