async reduce

asyncReduce.js

async function asyncReduce(array, asyncReducerFunction, initialValue) {
  let accumulator = initialValue;

  for (const element of array) {
    accumulator = await asyncReducerFunction(accumulator, element);
  }

  return accumulator;
}

// --- Example usage: --- //
const storeItems = [
  { id: 1, qty: 2, price: 30 },
  { id: 2, qty: 3, price: 50 },
  { id: 3, qty: 5, price: 40 },
];

const cartItems = [
  { id: 1, qty: 2 },
  { id: 4, qty: 3 },
  { id: 3, qty: 5 },
];

async function fetchProduct(id) {
  // Simulate a network request, e.g., fetching data from an API
  await new Promise((resolve) => setTimeout(resolve, 1000));

  return storeItems.find((storeItem) => storeItem.id === id);
}

async function main() {
  const totalPrice = await asyncReduce(cartItems, async (total, cartItem) => {
      const storeItem = await fetchProduct(cartItem.id);

      return total + cartItem.qty * (storeItem?.price ?? 0);
    }, 0);

  console.log(totalPrice);
  
  // Another way use async reduce with built in method
  const totalPrice2 = await cartItems.reduce( async (totalPromise, cartItem) => {
    const total = await totalPromise;
    
    const storeItem = await fetchProduct(cartItem.id);
    return total + cartItem.qty * (storeItem?.price ?? 0);
  }, Promise.resolve(0));
  
  console.log(totalPrice2);
}

main();