What is Callback Hell and how to avoid it? | Node.js Interview Questions

What You'll Learn

What callback hell is
Why it's problematic
How to avoid it

What is Callback Hell?

Callback Hell (Pyramid of Doom) occurs when you have nested callbacks, making code hard to read and maintain.

Example of Callback Hell

code.jsJavaScript

// ❌ Callback Hell
getUser(userId, (err, user) => {
  if (err) handleError(err);
  getOrders(user.id, (err, orders) => {
    if (err) handleError(err);
    getOrderDetails(orders[0].id, (err, details) => {
      if (err) handleError(err);
      getProduct(details.productId, (err, product) => {
        if (err) handleError(err);
        console.log(product);
      });
    });
  });
});

Solutions

1. Promises

code.jsJavaScript

getUser(userId)
  .then(user => getOrders(user.id))
  .then(orders => getOrderDetails(orders[0].id))
  .then(details => getProduct(details.productId))
  .then(product => console.log(product))
  .catch(handleError);

2. Async/Await

code.jsJavaScript

async function getData(userId) {
  try {
    const user = await getUser(userId);
    const orders = await getOrders(user.id);
    const details = await getOrderDetails(orders[0].id);
    const product = await getProduct(details.productId);
    console.log(product);
  } catch (error) {
    handleError(error);
  }
}