function isParallelogram (arr) {
  var arr1 = []
  var arr2 = []
  for (let i = 0; i < 4; i++) {

  }
  for (let i = 0; i < 4; i++) {
    for (let j = i + 1; j < 4; j++) {
      var distance = (arr[i].x - arr[j].x) * (arr[i].x - arr[j].x) + (arr[i].y - arr[j].y) * (arr[i].y - arr[j].y)
      arr1.push({
        points: [arr[i], arr[j]],
        distanceTag: [i, j],
        distance
      })
    }
  }
  arr1.sort(function (a, b) {
    return b.distance - a.distance
  })
  // 中點都除以2 所以省略除2
  var midpoint1 = {
    x: arr1[0].points[0].x + arr1[0].points[1].x,
    y: arr1[0].points[0].y + arr1[0].points[1].y
  }

  for (let i = 0; i < 4; i++) {
    if (!arr1[0].distanceTag.includes(i)) {
      arr2.push(arr[i])
    }
  }
  var midpoint2 = {
    x: arr2[0].x + arr2[1].x,
    y: arr2[0].y + arr2[1].y
  }
  if (midpoint1.x === midpoint2.x && midpoint1.y === midpoint2.y) {
    return true
  }
  return false
}