stock.js

function inAndOut(prices) {
    let high = prices[0];
    let low = prices[0];
    let lowIndex = 0;
    let bestGap = 0;
    const bestIndexes = [];
    const currentGap = () => high - low;

    for (var i = 1; i < prices.length; i++) {
        if (prices[i] < low) {
            // new slope; set new low, reset high.
            low = prices[i];
            lowIndex = i;
            high = prices[i];
        }

        else if (prices[i] > high) {
            // new peak on current slope
            high = prices[i];

            if (currentGap() > bestGap) {
                // new best
                bestGap = currentGap();
                bestIndexes[0] = lowIndex;
                bestIndexes[1] = i;
            }
        }
    }
    return bestIndexes;
}