React's event system uses internally a wrapper, called SyntheticEvent, around the native HTML DOM events for cross-browser support. React events follow the W3C spec, which can be found at https://www.w3.org/TR/DOM-Level-3-Events/.
React event names are camel-cased as opposed to HTML DOM events, which are lowercased. For instance, the HTML DOM event onclick would be called onClick in React. For a complete list of supported events, visit the React official documentation about events: https://reactjs.org/docs/events.html