Solving the undefined Issue in Async Functions for Node.js and Mongoose

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In this post, we will explore the issue through an example and provide effective solutions to ensure that your functions return the desired results.

The Problem: Function Returning undefined

Consider the following function designed to find a document in a database based on a name property provided in rowObj.

[[See Video to Reveal this Text or Code Snippet]]

What Happens Here?

The findDoc function attempts to return docs, but the return statement is inside a callback. JavaScript does not work this way—the outer function does not wait for the inner callback to resolve.

As a result, when you log searchDoc, it outputs undefined.

Alternative Behavior

[[See Video to Reveal this Text or Code Snippet]]

This demonstrates that the code is working, but the design of the function prevents it from returning the value correctly.

The Solution: Using Callbacks or Async/Await

To fix this issue and ensure that your function returns the expected value, you have two main options: using callbacks or async/await.

1. Using Callbacks

You can modify the findDoc function to accept a callback function that processes the result:

[[See Video to Reveal this Text or Code Snippet]]

With this change, searchDoc will contain the correct document when the callback is invoked.

2. Using Async/Await

If you prefer working with async/await for cleaner and more readable code, you can refactor your function to return a Promise:

[[See Video to Reveal this Text or Code Snippet]]

Now, findDoc returns a Promise, allowing you to use await conveniently. This keeps your code neat and synchronous in style.

Conclusion

Happy coding!