Função para concatenar objetos JavaScript

concat_obj.js

var demand_cost = [
  { peak_demand: 500, off_peak_demand: 800 },
  { peak_demand: 1500, off_peak_demand: 1800 },
];
var energy_cost = [
  { peak_energy: 600, off_peak_energy: 900 },
  { peak_energy: 1600, off_peak_energy: 1900 },
];

function concat_obj(...arrays_obj) {
  let new_arr_of_obj = Array.from({ length: arrays_obj[0].length }, () => ({}));
  [...Array(arrays_obj.length).keys()].forEach((array_index) => {
    arrays_obj[array_index].forEach((el, index_el) => {
      Object.keys(el).forEach((key) => {
        new_arr_of_obj[index_el][key] = el[key];
      });
    });
  });
  return new_arr_of_obj;
}
const costs = concat_obj(demand_cost, energy_cost);
console.log(demand_cost, energy_cost);