title: OpenCV.js - iterate through contours hierarchy
body: <p>I've read the OpenCV.js documentation for <code>cv.findContours()</code>, but I cannot find a way of accessing the hierarchy (parent, children, next, prev) object. </p>
  
  <p><a href="https://docs.opencv.org/3.4/da/d0a/tutorial_js_contours_hierarchy.html" rel="nofollow noreferrer">https://docs.opencv.org/3.4/da/d0a/tutorial_js_contours_hierarchy.html</a></p>
  
  <p>How would one iterate through the <code>hierarchy</code> object in JavaScript?</p>
  
  <p>I'm using <code>cv.RETR_TREE</code> contour retrieval mode.</p>