function closestSquaredDistanceXY(extent, x, y) {
  let dx, dy;
  if (x < extent[0]) {
    dx = extent[0] - x;
  } else if (extent[2] < x) {
    dx = x - extent[2];
  } else {
    dx = 0;
  }
  if (y < extent[1]) {
    dy = extent[1] - y;
  } else if (extent[3] < y) {
    dy = y - extent[3];
  } else {
    dy = 0;
  }
  return dx * dx + dy * dy;
}
@param {Extent} extent Extent.
@param {number} x X.
@param {number} y Y.
@return {number} Closest squared distance.