AppleStocks.js

function getMaxProfit(stockPricesYesterday) {

    let buy = stockPricesYesterday[0], sell = stockPricesYesterday[1];

    for(let i = 1; i < stockPricesYesterday.length - 1; i++) {
        if(stockPricesYesterday[i] < buy) {
            buy = stockPricesYesterday[i];
        }
        if(stockPricesYesterday[i+1] > sell) {
            sell = stockPricesYesterday[i+1]
        }
    }
 
    return sell - buy;
}

console.log(getMaxProfit([10,11,5,8,11,9]));