### Summary: overlayRef and contentRef are undefined on componentDidMount, but have the correct value on componentDidUpdate. ### Steps to reproduce: 1. Set the overlayRef and contentRef prop on ReactModal. 2. console.log the value of overlayRef and contentRef inside componentDidMount. 3. The values will be undefined. ### Expected behavior: overlayRef and contentRef should hold the correct values on componentDidMount. ### Link to example of issue: https://codesandbox.io/s/qq9kpwxxp9