Events are categorized based on their function, property, usage and etc. So you may have seen different type of event categories. In here our main focus is to deal with events. Some events can be easily handle inside reactjs using ES6 syntax, but some may not. For example "onClick", "onChange" events can be handle easily. Some events like "onScroll" event trigger in document level on scrolling a "Div".
If you want to catch scrolling your webpage and do some stuff, how to do that. It is so simple than you think. First of all add window event listener to "componentDidMount" function.