從目標體脂推算理想體重與需減去的脂肪，用法為 weight( 100, 0.3, 0.2, 400 )

weight.js

function weight(
	currentWeight = 82,
	currentRatio = 0.23,
	targetRatio = 0.2,
	dailyBurn = 400,
) {
	const currentFat = currentWeight * currentRatio
	const currentMuscle = currentWeight - currentFat
	const targetWeight = currentMuscle / (1 - targetRatio)
	const loseFat = currentWeight - targetWeight // kg
	const calories = 7700 * loseFat // 大卡
	const estimatedDays = Math.round(calories / dailyBurn)

	return {
		currentFat,
		currentMuscle,
		targetWeight,
		loseFat,
		estimatedDays: `${Math.floor(estimatedDays / 30)}month ${estimatedDays % 30}days`,
	}
}