example.js

  const orderItemListPromises = orderItemList.map(orderItems => {
    return Promise.all(
      orderItems.data.map(async orderItem => {
        const filter = { where: { orderId: orderItem.order_id } };
        const dateString = orderItem.date + "";
        const stadistics = {
          shopId: orderItem.shopId,
          date: parseInt(dateString.slice(0, -3)),
          itemName: orderItem.item_name,
          amount: orderItem.total,
          quantity: orderItem.quantity,
          finished: 0
        };

        try {
          const receipt = await axios.get(
            url +
              "/" +
              orderItem.shopId +
              "/receipts?filter=" +
              JSON.stringify(filter),
            { headers }
          );

          if (receipt.data.length > 1) {
            console.log(
              "¡¡¡¡¡ALERTA!!!!! orderId duplicado x" + receipt.data.length
            );
          }

          if (!receipt.data[0].workerName) {
            stadistics.worker = "Desconocido";
          } else {
            stadistics.worker = receipt.data[0].workerName;
          }

          console.log("SAVE", stadistics);
          listStatsToSave.push(stadistics);
          console.log("listStatsToSave ", listStatsToSave);
        } catch (error) {
          return;
        }
      })
    );
  });

  await Promise.all(orderItemListPromises);

  console.log("XX", listStatsToSave);
  console.log("XX", listStatsToSave.length);

example2.js

  const orderItemListPromises = orderItemList.map(orderItems => {
    return Promise.all(
      orderItems.data.map(async orderItem => {
        const filter = { where: { orderId: orderItem.order_id } };
        const dateString = orderItem.date + "";
        const stadistics = {
          shopId: orderItem.shopId,
          date: parseInt(dateString.slice(0, -3)),
          itemName: orderItem.item_name,
          amount: orderItem.total,
          quantity: orderItem.quantity,
          finished: 0
        };

        try {
          const receipt = await axios.get(
            url +
              "/" +
              orderItem.shopId +
              "/receipts?filter=" +
              JSON.stringify(filter),
            { headers }
          );

          if (receipt.data.length > 1) {
            console.log(
              "¡¡¡¡¡ALERTA!!!!! orderId duplicado x" + receipt.data.length
            );
          }

          if (!receipt.data[0].workerName) {
            stadistics.worker = "Desconocido";
          } else {
            stadistics.worker = receipt.data[0].workerName;
          }

          return stadistics;
        } catch (error) {
          return;
        }
      })
    );
  });

  const result = await Promise.all(orderItemListPromises);

  result.reduce((acc, current) => {
    // Aquí haces tus cosas
  });

example3.js

// const data = require("./data");
const data = [
  /** El enorme array **/
];

function groupBy(group) {
  return function(acc, entry) {
    const result = {
      shopId: entry.shopId,
      date: entry.date,
      worker: entry.worker,
      itemName: entry.itemName,
      finished: entry.finished
    };

    delete result[group];

    if (!acc.has(entry[group])) {
      result.amount = entry.amount;
    } else {
      const { amount } = acc.get(entry[group]);
      result.amount = amount + entry.amount;
    }

    acc.set(entry[group], result);

    return acc;
  };
}

const groupedByWorker = data.reduce(groupBy("worker"), new Map());
const groupedByItem = data.reduce(groupBy("itemName"), new Map());

const groupedByWorkerArray = Array.from(groupedByWorker).map(
  ([worker, entry]) => ({ worker, ...entry })
);

const groupedByItemArray = Array.from(groupedByItem).map(
  ([itemName, entry]) => ({ itemName, ...entry })
);

console.log("BY WORKER", groupedByWorkerArray);
console.log("BY ITEM", groupedByItemArray);