This function calculates change percentage between 2 pairs of values and accumulates the average and the last iterated value as previous value in the next iteration.

AccumulativeAverageChangePercentage.js

calculateAccumulativeAverageChangePercentage(set, initial) {
        let deltaObj = set.reduce((total, currentValue) => {
            let currentChange = (currentValue - total.prevValue) / Math.abs(total.prevValue);
            let averageMode = total.change != 0 ? 2 : 1;
            return {
                change: (currentChange + total.change) / (averageMode),
                prevValue: currentValue
            };
        }, {change: 0, prevValue: initial});

        deltaObj.change = Math.abs(deltaObj.change) * 100;
        return deltaObj;
}

calculateAccumulativeAverageChangePercentage(set, initial) {
        return set.reduce((total, currentValue) => {
            let currentChange = (currentValue - total.prevValue) / Math.abs(total.prevValue);
            let averageMode = total.change != 0 ? 2 : 1;

            Object.assign(total,  {
                change: Math.abs((currentChange + total.change) / averageMode) * 100 ,
                prevValue: currentValue
            });

            return total;
        }, {change: 0, prevValue: initial});
}