Node.js vs. C++ library

Use Blynk with Node.js

Node.js is easy to write scripts, update, and prototype. It also supports secure SSL connection out-of-the-box.
Node.js has lots of modules for Raspberry Pi, BeagleBone, Desktop Ubuntu etc - which makes integration very easy.
Node.js has timers, asynchronous operations, etc - this is important when you start building more complex applications.

Use Blynk with C++

If you want just to toggle a pin, it will simply work out-of-the-box. But if you want to add more functionality, it will require some Linux, threading, sockets knowledge, modifying Makefile, etc. So, C++ is generally for advanced developers.
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