toFixed after using reduce method JS

Question

I`m maping through an array and reducing 50 items to 1 - their sum. That 50 items are float precision numbers. Please help, I don`t understand where in that map I should put toFixed(2), to get proper summaryIncome property instead something like this: 39990,89999999999913.

var data = [
  {id: 1, incomes: [{value:1}, {value: 2}]}, 
  {id: 2, incomes: [{value:2}, {value: 3}]}],
  ...
]

var summary = data.map(item => ({
  ...item,
  summaryIncome: item.incomes.reduce((acc, income) =>
    acc += income.value, 0)
}));

Answer 1

To keep the sum accurate, call toFixed after summing up all the values:

var data = [
  {id: 1, incomes: [{value: 0.1}, {value: 0.2}]}, 
  {id: 2, incomes: [{value:2}, {value: 3}]},
]

var summary = data.map(item => ({
  ...item,
  summaryIncome: item.incomes.reduce((acc, income) => acc + income.value, 0).toFixed(2)
}));
console.log(summary);

To only put decimal points if necessary:

var data = [
  {id: 1, incomes: [{value: 0.1}, {value: 0.2}]}, 
  {id: 2, incomes: [{value:2}, {value: 3}]},
]

var summary = data.map(item => ({
  ...item,
  summaryIncome: (() => {
    const trueSum = item.incomes.reduce((acc, income) => acc + income.value, 0);
    return Number.isInteger(trueSum) ? String(trueSum) : trueSum.toFixed(2);
  })()
}));
console.log(summary);