There are several advantages of using JavaScript Node.js over PHP. Here I'll discuss only three of this advantages
Speed: It is believe that JavaScript Node.js is far more faster than PHP in terms of handling request much especial for a website with a huge amount of data, that is why some popular e-Commerce website like ebay/paypal and walmart migrate to using node.js as it server side programming language.
Node.js is easier to learn if you already have a knowledge of javaSript in designing client side application.
It is event-driven and very good at handling concurrent request when compare to PHP