Simple function to get distance between two points with an added twist --- in order to prevent performance problems with squaring large numbers and getting the square root of their addition, the smallest x and y values are set as zero and the largest are set as the difference between the two points. This way, the performance is better.

distancebetweentwopoints.js

function distancebetweentwopoints(x1, y1, x2, y2) {
      if (x1 > x2) {
          x1 = x1 - x2;
          x2 = 0;
      } else {
          x2 = x2 - x1;
          x1 = 0;
      }
      if (y1 > y2) {
          y1 = y1 - y2;
          y2 = 0;
      } else {
          y2 = y2 - y1;
          y1 = 0;
      }
      var xs = Math.pow(x2 - x1, 2);
      var ys = Math.pow(y2 - y1, 2);
      return Math.sqrt( xs + ys );
}