Question 1

Why does my async function return a Promise instead of a value?

Accepted Answer

This is the defining behaviour of async functions rather than a mistake. Declaring a function async wraps its return value in a promise automatically. Returning a number from an async function produces a promise that resolves to that number, and there is no way to make it return the number directly, because the point of the construct is that the result may not exist yet.

To get the value you have to wait for it, which means either awaiting the call inside another async function or attaching a handler to the promise. Forgetting this produces a recognisable symptom: logging the result shows a pending promise rather than the data, and passing it onward causes downstream code to fail on a value that is not the shape it expected.

A few specific traps recur.

- Calling an async function without awaiting it, usually because the calling function was not itself marked async. The call still runs, but execution continues immediately and the result is never collected.
- Using an async callback inside an array method that does not understand promises. Mapping with an async callback produces an array of promises rather than an array of values. Waiting on all of them together converts it back.
- Awaiting inside a loop when the operations are independent. This is correct but runs them one after another, which can be dramatically slower than starting them together and waiting once at the end.

There is also a correctness hazard worth knowing. An unawaited promise that rejects becomes an unhandled rejection, which in modern runtimes can terminate the process. Awaiting is therefore not only about collecting the value, it is also about ensuring failures are attached to something able to handle them.

Question 2

Why does my Node app crash with an unhandled promise rejection?

Accepted Answer

A promise that rejects with nothing attached to handle it produces an unhandled rejection, and modern Node treats that as fatal by default. The process exits. This changed from earlier versions where

Question 3

What causes Cannot read properties of undefined in JavaScript?

Accepted Answer

The error means you accessed a property on a value that was undefined or null. Modern engines name the property in the message, and that name is the most useful clue available, because it tells you

Question 4

What is the event loop in Node.js?

Accepted Answer

Node runs your JavaScript on a single thread. It achieves concurrency not by running code in parallel but by never waiting: operations that would block, such as reading a file or making a network

Question 5

What are the best practices for error handling in Node.js applications?

Accepted Answer

Implementing Node.js error handling best practices improves application reliability and user experience. Key methods include try-catch blocks, centralized error handling, and logging.

Question 6

Why does this become undefined inside a callback in JavaScript?

Accepted Answer

In JavaScript the value of this is determined by how a function is called, not by where it was written. When you pass a method somewhere as a callback, you pass the function itself and leave the

Question 7

What is the difference between synchronous and asynchronous code?

Accepted Answer

Synchronous code runs one statement after another, and each waits for the previous to finish. Asynchronous code starts an operation and continues without waiting, handling the result when it arrives.

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