en.javascript.info/1-js/4-data-structures/9-array-iteration/2-partial-sums-array/_js.view/solution.js

function getSums(arr) {
  var result = [];
  if (!arr.length) return result;

  var totalSum = arr.reduce(function(sum, item) {
    result.push(sum);
    return sum + item;
  });
  result.push(totalSum);

  return result;
}