Javascript Subtract between two arrays of objects

Hi can anybody help me to implement the right/clean way of subtracting between two arrays of object. My case (backend) is that I fetch Products data from mongodb, then I also have Trolley data that is fetched from MySql, what I’m trying to do is that if product stock is subtracted by quantity in trolley & the result is lower then 0 then I will throw error. Right know my Implementation as below:

 const trolleyProducts = await Trolley.findAll({
    where: {
      userId,
      isActive: true,
    },
    attributes: ["id", "productId", "quantity", "notes"],
  });
 
 const products = await ProductModel.find(
    {
      dbId: trolleyProductIds,
    },
    {
      _id: 0,
      sku: 0,
      barcode: 0,
      reservedStock: 0,
      sold: 0,
      tags: 0,
      infos: 0,
      photosURL: 0,
    }
  );
  
  // ******* here is my implementation *******
  products.map((product) => {
    trolleyProducts.map((trolley) => {
      if (product.dbId === trolley.productId) {
        if (product.stock - trolley.quantity < 0) {
          throw {
            name: "Bad Request",
            message: " Stock is less than desired quantity",
          };
        }
      }
    });
  });
  // **************

Please let me know if there are better & cleaner approach then mine (for performance matter). Thanks 🙂

Answer

You can convert trolleyProducts to an object whose keys are the product IDs. That way you won’t need a nested loop to find the matching product.

Also, map() should be used when the callback function returns a value and you’re making an array of those values. Use forEach() if the loop is for side effect only.

const trolleyProducts = await Trolley.findAll({
  where: {
    userId,
    isActive: true,
  },
  attributes: ["id", "productId", "quantity", "notes"],
});
// convert array to object.
trolleyProducts = Object.fromEntries(trolleyProducts.map(obj => [obj.productId, obj]));

const products = await ProductModel.find({
  dbId: trolleyProductIds,
}, {
  _id: 0,
  sku: 0,
  barcode: 0,
  reservedStock: 0,
  sold: 0,
  tags: 0,
  infos: 0,
  photosURL: 0,
});

products.forEach((product) => {
  const trolley = trolleyProducts[product.dbId]
  if (trolley && product.stock - trolley.quantity < 0) {
    throw {
      name: "Bad Request",
      message: `Stock is less than desired quantity for ${product.dbId}`,
    };
  }
});