Centroid of a polygon script

Question

I've read other examples on here on finding the centroid of a polygon, I do not see where I am going wrong, why my centroid is so far off. If someone could please explain to me where my calculation is off.

I came up with this solution:

function getCentroid() {
  var coords = getCoords();
  var signedArea = 0;
  var x = 0;
  var y = 0;
  
  for (var i = 0; i < coords.length - 1; i++) {
    var temp = (coords[i].x * coords[i + 1].y) - (coords[i + 1].x * coords[i].y);
    
    signedArea += temp;
    x += (coords[i].x + coords[i + 1].x) * temp;
    y += (coords[i].y + coords[i + 1].y) * temp;
  }
  
  signedArea *= 0.5;
  x /= 6 * signedArea;
  y /= 6 * signedArea;
  
  return "" + Math.round(x) + "," + Math.round(y);
}

getCoords() returns a JSON array in this form:

[
   {
      "x":"600",
      "y":"124"
   },
   {
      "x":"560",
      "y":"396"
   },
   {
      "x":"994",
      "y":"370"
   },
   {
      "x":"918",
      "y":"121"
   },
   {
      "x":"600",
      "y":"124"
   }
]

The function getCentroid() returns the centroid (or atleast it should) of the polygon as a commaseperated string in the form: x,y

However, what it is returning is so far off the center.

returns: 312239,219226

Can anyone point me in the right direction?

Answer 1

Silly me, I didn't realize that the values of the coordinates were stored as strings in the json array. I casted them to Numbers and all is well.