{
  scroll: {
    changed: Boolean,
    left: Integer,
    right: Integer,
    top: Integer,
    bottom: Integer,
    velocity: {
      x: Integer,
      y: Integer
    }
  },
  size: {
    changed: Boolean
    x: Integer,
    y: Integer,
    docY: Integer
  },
  mouse: {
    changed: Boolean,
    x: Integer
    y: Integer
    velocity: {
      x: Integer
      y: Integer
    }
  }
}

// From robb0wen/tornis
// import the Tornis store functions
import {
  watchViewport,
  unwatchViewport,
  getViewportState
} from 'tornis';

// define a watched function, to be run on each update
const updateValues = ({ size, scroll, mouse, orientation }) => {
  if (size.changed) {
    // do something related to size
  }

  if (scroll.changed) {
    // do something related to scroll position or velocity
  }

  if (mouse.changed) {
    // do something related to mouse position or velocity
  }
};

// bind the watch function
// By default this will run the function as it is added to the watch list
watchViewport(updateValues);

// to bind the watch function without calling it
watchViewport(updateValues, false);

// when you want to stop updating
unwatchViewport(updateValues);

// to get a snapshot of the current viewport state
const state = getViewportState();