Version 6.0 up:

You can do this in simple way:

const polygon = new Polygon(fabricPoints, {
 fill: 'rgba(255, 0, 0, 0.5)',
 stroke: 'black',
 strokeWidth: 2,
 selectable: true,
 hasControls: true,
 hasBorders: true,
});

polygon.setBoundingBox(); //this will recalculate bounding box