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export default function(ring) { var i = 0, n = ring.length, area = ring[n - 1][1] * ring[0][0] - ring[n - 1][0] * ring[0][1]; while (++i < n) area += ring[i - 1][1] * ring[i][0] - ring[i - 1][0] * ring[i][1]; return area; }