Wait for async forEach that in a callback function to finished then return data

Question

I'm a newbie in asynchronous javascript. I want to use an async forEach with Promise Array method but In javascript await is only valid for the async function but we can not mark a callback function as an async. I know I make a logical mistake. How can achieve that? Any Help?

Also you can give me an advise about that if-else hell. How can I avoid that if-else hell.

My try with Promise Array:

router.get("/", async (req, res) => {
  const token = req.cookies.jwt;
  let cartObjects = [];
  cartRequests.getCart( token, (cartError, cartData) => {
    if (cartError) {
      return res.status(400).render('error', {message: cartError})
    }    

    if(cartData.error)
    {
      if (cartData.error==="There is no cart created for this user") {
        return res.status(200).render("cart/cartPage", { cartObjects });
      }
      else if(cartData.error === "Invalid Token"){
        return res.status(200).render('error', {message: 'Not authenticated.'})
      } else{
        return res.status(400).render('error', {message: cartData.error})
      }
      
    }

    const cartItems = cartData.items;
    let cartItemIndex = 0;
    let promises = []

    cartItems.forEach(async (item) => {
      let productId = item.productId;
       promises.push( new Promise((resolve, reject) => {
        productRequets.getProductById(productId, (productErr, productData) => {
          if (productData.error) {
            reject(productData.error);
          } else {
            let cartObject = getCartObject(
              productData,
              cartItems,
              cartItemIndex
            );
            resolve(cartObject);
          }
        });
      }))
        .catch((err) => {
          
        })
        .then((resolvedData) => {
          cartObjects.push(resolvedData);
        });
    });
    
    await Promise.all(promises)
    return res.status(200).render("cart/cartPage", { cartObjects });
  });
});

_"we can not mark a callback function as an async"_ That's wrong. You can. You even did it in your code. But `forEach` won't wait. Do you want to each array element to wait for the previous element or do you want to wait for all promises? In the latter case you use `map` instead of `forEach` and map each element to a promise. — jabaa, Mar 19 '22 at 13:20
You probably need to create an array of promises and then use the `Promise.all` method. — tromgy, Mar 19 '22 at 13:24
Replace `forEach` with `map` and return a promise. Then you can await all elements with `Promise.all`. — jabaa, Mar 19 '22 at 13:24
When I try to achieve with Promise.all program returns an error: await Promise.all(promises) ^^^^^ SyntaxError: await is only valid in async function — AssSoonAsPossiblee, Mar 19 '22 at 13:26
The callback in your request handler has to be async: `router.get("/", async (req, res) => {` — jabaa, Mar 19 '22 at 13:27
I have added async but I still get the same error, what is wrong I have edited post with new code. — AssSoonAsPossiblee, Mar 19 '22 at 13:32
@Quentin I saw that question but I cant figure out the solution — AssSoonAsPossiblee, Mar 19 '22 at 13:44
@AssSoonAsPossiblee — Well the accepted answer very clearly says "you cannot use forEach" and you're still trying to use forEach, so start there. — Quentin, Mar 19 '22 at 13:45

Wait for async forEach that in a callback function to finished then return data

0 Answers0