fuckThisWorld.js

var arr = [
    {ccy:"EUR", balance:1000},
    {ccy:"USD", balance:"2700"},
    {ccy:"EUR", balance:"5600"},
    {ccy:"USD", balance:"2500"}
  ] 

var newArr = [];

arr.reduce(function(previousValue, currentValue, index, array) {
  if (index === 0) newArr.push({y: +currentValue.balance, name:currentValue.ccy})
  if (index > 0) {
    var mark = 0;
    for (var i = 0; i < newArr.length; i += 1) {
      if (newArr[i] && newArr[i].name === currentValue.ccy) {
         newArr[i].y += +currentValue.balance;
         mark = 1;
      }
    }
    if (!mark) newArr.push({y:+currentValue.balance, name:currentValue.ccy});
  }
}, newArr)