// 各取引所の価格の宣言
let prices = [800000, 810000, 890000]
let volumes = [1000, 50000, 3000]
// 加重平均を取得
let toalAmount = prices.map((price,i) => price * volumes[i]).reduce((prev, x) => prev + x)
let tovalVolume = volumes.reduce((prev, x) => prev + x)
let average = toalAmount / tovalVolume
// 平均の距離から重みを算出
let diffList = prices.map((price) => 1 / Math.pow(price - average, 2))
let totalDiff = diffList.reduce((diff,x) => diff + x)
let weightList = diffList.map((diff) => diff / totalDiff)
// 価格に重みを加えてインデックス価格を算出
let indexPrice = prices.map((price, index) => price * weightList[index]).reduce((price, x) => x + price)
console.log(indexPrice) // 809414.8241857525