Part 2 - Setting this.from and this.to for the exiting transition

Post.js

onExit = () => {
  // we don't want the code to run if there is no
  // preview element to transition to.
  if (!this.preview) return;
  
  this.from = {
    top: 0,
    height: this.post.offsetHeight,
    width: this.post.offsetWidth,
    borderRadius: this.postStyler.get('borderRadius')
  };
  this.to = this.getPreviewStyleAndPosition();
};