React CSS Transitions - codepen.io examples

linklist.md

http://codepen.io/anon/pen/VvzZWr - CSS only hover transition

http://codepen.io/anon/pen/WQOVbE - React hover transition

http://codepen.io/anon/pen/jbLPBo - React button toggle

http://codepen.io/anon/pen/dYzYyj - React creating boxes

http://codepen.io/anon/pen/gaxaxY - VanillaJS creating boxes

http://codepen.io/anon/pen/EVvVmQ - React creating + deleting boxes

http://codepen.io/anon/pen/WQEQEx - VanillaJS creating + deleting boxes

http://codepen.io/anon/pen/dYzMBe - React official transition example

http://codepen.io/anon/pen/EVvKqv - React official transition example at initial mounting

http://codepen.io/kenwheeler/pen/PqWajd - React + Radium simple button example

What is this line doing: window.getComputedStyle(this.element).opacity ? It doesn't seem to be assigning to anything and if I remove the line the transition stops working. It's also throwing a warning in my console.