The simplest way is to convert it to JSON which is a platform and language-agnostic string format and pass that to your C++ where it can then parse the JSON string into its own data format.
If your C++ code is running it its now process, you will then have to find a way to deliver the string to the other process. If the C++ code is in a child process, you can send it over stdio. If not, then you will need some other interprocess communication mechanism for sending the string to app running the C++ code.
There is a mechanism for creating a nodejs add-on in C++ where you can exchange data between the two and the C++ code runs in the nodejs process, but it is not for the faint of heart as its fairly involved and difficult to learn. The doc for addons is here. It will, in general, be a lot, lot simpler to send a JSON string between two processes.
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