SOURCE

let points =[
  {x:1,y:3},
  {x:-1,y:-4}
]
points.dist = function(){
  let p1 = this[0];
  let p2 = this[1];
  let a = p2.x -p1.x;
  let b = p2.y -p1.y;
  return Math.sqrt(a*a +b*b);
};
points.dist()
// console.log(points)
console.log(points.dist())
console.log(typeof(points.dist))