Difference fails on shared edge case

[w8r]

const polygon1 = {
    'type': 'Polygon',
    'coordinates': [
      [[ 10, 10 ], [ 80, 10 ], [ 80, 80 ], [ 10, 80 ], [ 10, 10 ]]
    ]
  };

  const polygon2 = {
    'type': 'Polygon',
    'coordinates': [
      [[ 20, 10 ], [ 30, 10 ], [ 30, 80 ], [ 20, 80 ], [ 20, 10 ]]
    ]
  };

https://codepen.io/w8r/pen/NMQZMq