Using JS to convert JSON object key : value pairs to summarised JSON of values

I am using JavaScript and currently I have

filteredObj = 
    [{Amount: 100, Country: "England"},
    {Amount: 100, Country: "England"},
    {Amount: 200, Country: "England"},
    {Amount: 300, Country: "China"},
    {Amount: 200, Country: "China"},
    {Amount: 100, Country: "England"},
    {Amount: 400, Country: "England"},
    {Amount: 300, Country: "China"}]

How can I convert this to

   condensedObj =  [{China: 800,
                     England: 900}]

The following combines the code but keeps them in separate {}s i.e.

 condensedObj = 
[{Country: "China",
  Amount:  800},
  {country: "England",
   Amount: 900}]

Current code:

condensedObj = filteredObj
    .reduce(
      function (res, obj) {
        if (!(obj['Country'] in res))
          res.__array.push(
            (res[obj['Country'] = obj)
          );
        else {
          res[obj['Country'].Amount +=
            obj.Amount;
        }
        return res;
      },
      { __array: [] }
    )
    .__array.sort(function (a, b) {
      return b.Amount - a.Amount;
    });

Thanks!

Answer

You can use .reduce to create an object with Country as keys and the sum of Amount as values
Then, sort these pairs according to the value (Amount) as follows:

const arr = [
  { Amount: 100, Country: "England" },
  { Amount: 100, Country: "England" },
  { Amount: 200, Country: "England" },
  { Amount: 300, Country: "China" },
  { Amount: 200, Country: "China" },
  { Amount: 100, Country: "England" },
  { Amount: 400, Country: "England" },
  { Amount: 300, Country: "China" }
];

const countries = arr.reduce((acc, {Amount,Country}) => 
  ({ ...acc, [Country]: (acc[Country] || 0) + Amount })
, {});
const sorted = Object.fromEntries(
  Object.entries(countries).sort(([,amountA],[,amountB]) => amountA - amountB)
);
const res = [ sorted ];

console.log(res);

References:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/Reduce

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/entries

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/sort

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/fromEntries