```js
function maxStockProfit(pricesArr) {

  const Price = {
    'buy': 0,
    'sell': 0,
    'change': true
  };
  
  
  return pricesArr.reduce((maxProfit, currentPrice, indx, arr)=> {
    Price.buy = (Price.change) ? currentPrice : Price.buy;
    Price.sell = arr[indx+1];
    
    if(Price.sell < Price.buy) {
      Price.change = true;
    } else {
      let tempProfit = Price.sell - Price.buy;
      maxProfit =  (tempProfit > maxProfit) ? tempProfit : maxProfit;
      Price.change = false;
    }
    
    return maxProfit;
  }, -1);
  
  
}

console.log(maxStockProfit([10,18,4,5,9,6,16,12]));
```