You use React APIs to do everything you would normally do with React. You use the API directly if you don't have a build step for your web app and you cant or don't want to add one. Since React is indeed simply a library with an API, you can progressively integrate React into an existing web app in this way (a big selling point in the early days that people have sensibly forgotten by now). You couldn't progressively integrate a traditional framework like Django for example.
Lifecycle methods like render, componentWillMount, etc are just callbacks that get fired when you render you a component. I don't think any library is immediately graduated to the class of "framework" the moment a callback is added.
Lifecycle methods like render, componentWillMount, etc are just callbacks that get fired when you render you a component. I don't think any library is immediately graduated to the class of "framework" the moment a callback is added.