I was inspecting some source code until I notice this weird variable declaration which I don't understand fully.
let eventsEnabled : ?boolean = null;
What this means?
Source code from here: https://github.com/facebook/react/blob/v16.0.0-alpha.3/src/renderers/dom/fiber/ReactDOMFiber.js#L83
React uses Flow, a static type checker
?boolean
is signifying that eventsEnabled
is a maybe type, meaning that it can be a boolean, or undefined
/null
.