title: How to call a function when d3.brush is cleared?
body: <p>To elaborate on this, let's say we have a typical d3 brush use case, something like the <a href="https://bl.ocks.org/mbostock/6232620" rel="nofollow noreferrer">example here by Mike Bostock</a>.
  The brush gets cleared when I click anywhere outside the brush. So I wish to execute a function when that event gets fired.
  The relevant code is pretty along the lines of Mike's example.</p>