ReasonML Quick Start Guide

React ref 

The React ref is just an instance variable of state:

type state = {  isOpen: bool,  touches,  width: ref(float),};

We attach the React ref on the <nav /> element by setting the ref property to the result of self.handle((ref, self) => ...):

ref={  self.handle((ref, self) =>    self.state.width :=      (        switch (Js.Nullable.toOption(ref)) {        | None => 0.0        | Some(r) => ReactDOMRe.domElementToObj(r)##clientWidth        }      )  )}

Since a React ref could be null in JavaScript, we convert it to an option and pattern match on its value.

The type of the React ref depends on whether it is a DOM element or a React component. The former's type is Dom.element, and the latter's is ReasonReact.reactRef. To convert a ReasonReact.reactRef to a JavaScript object, use  ...