determine the area of a polygon. using shoelace formula algorithm.

area-polyfill.js

Math.area = Math.area || function(polygon){
  const length = polygon.length;

  let sum = 0;

  for(let i = 0; i < length; i += 2){
    sum += polygon[i    ] * polygon[(i + 3) % length]
         - polygon[i + 1] * polygon[(i + 2) % length];
  }

  return Math.abs(sum) * 0.5;
}

usage.js

Math.area([
  0, 0,
  3, 0,
  0, 4
]); // 6