[nicoburns]

React is primarily (and almost exclusively) used as a frontend framework. In that context information sources are HTTP apis (and occasionally browser storage, but that deleted at anytime, so pretty much every app also stores data on a server somewhere).

There are lots of ways to connect to these APIs, but a common one with React is to a Redux middleware to do the fetching. Underneath everything, something will be using either the classic "XMLHttpRequest" or the newer "fetch api" to do the actual HTTP requests.