Calculate previous element as input to next element of array in JS?

Question

I have following code to calculate Stock value dynamic based on the previous calculated value

and also the only last value of element we have currentStock field which will be useful to calculate dynamic stock

this.stockList.map(function(product, index) {
 product.Data.map(function(attribute, currentIndex) {
   if (currentIndex == 0) {
     attribute.stock = attribute.currentStock;
   } else {
     const requestVal = (attribute.qty * attribute.unit) + attribute.stock;   // here i need to have a previous stock value 
     console.log("requestVal", attribute);
     attribute.stock = requestVal;
   }
 });
}); 

my sample expected array :

[
  {
    Product: ABC
    Data: [
      { "billDate": "1-apr-2016", "unit": 2, "Qty": 4, "Amount": 4500, "currentStock": 10 },
      { "billDate": "1-may-2016", "unit": 3, "Qty": 2, "Amount": 4500, "stock": (2 * 3) + 10 = 16 },
      { "billDate": "1-may-2016", "unit": 1, "Qty": 2, "Amount": 4500, "stock": (2 * 1) + 16 = 18 },
    ],
  },
]

Answer 1

Observation/Suggestion :

• It should be attribute.Qty instead of attribute.qty
• In second iteration, You can use product.Data[currentIndex - 1].stock to get the previous object stock value.

Try this :

const stockList = [
  {
    Product: 'ABC',
    Data: [
      { "billDate": "1-apr-2016", "unit": 2, "Qty": 4, "Amount": 4500, "currentStock": 10 },
      { "billDate": "1-may-2016", "unit": 3, "Qty": 2, "Amount": 4500 },
      { "billDate": "1-may-2016", "unit": 1, "Qty": 2, "Amount": 4500 },
    ],
  },
];

stockList.forEach(function(product, index) {
 product.Data.forEach(function(attribute, currentIndex) {
   if (currentIndex === 0) {
     attribute.stock = attribute.currentStock;
   } else {
     const requestVal = (attribute.Qty * attribute.unit) + product.Data[currentIndex - 1].stock;
     attribute.stock = requestVal;
   }
 });
});

console.log(stockList)