Скачать или смотреть Understanding Why Your async function Returns Undefined in JavaScript

Discover how to resolve the issue of an `async function` returning `undefined` in JavaScript, specifically with handling asynchronous calls and promises using Puppeteer.
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This video is based on the question https://stackoverflow.com/q/62848716/ asked by the user 'Shachar Oren' ( https://stackoverflow.com/u/7797264/ ) and on the answer https://stackoverflow.com/a/62848742/ provided by the user 'ΔO 'delta zero'' ( https://stackoverflow.com/u/3290062/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding Why Your async function Returns Undefined in JavaScript

JavaScript's async/await functionality allows you to work with asynchronous operations more easily by writing cleaner code, but sometimes things can go wrong. One common issue developers face is when an async function unexpectedly returns undefined. In this post, we'll explore a specific scenario and how to resolve it, so your code behaves as expected and retrieves the necessary data.

The Problem: Undefined Return Value from an Asynchronous Function

Let's consider a situation where you're trying to fetch product information from Amazon using a function called getQAfromAmazon(productID). You call this function with the intention of getting some data, but instead, you find that the result is:

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

This issue surfaces because your getQAfromAmazon() function does not properly return any value. Understanding why this is happening is crucial for resolving the problem.

The Cause of the Issue

The primary reason for receiving undefined in this context is that the return statement for the data you are attempting to retrieve (productInfo) exists deep within a promise chain. Specifically, the return productInfo; is nested inside a .then() method after calling puppeteer.launch(...).

Key Points to Note

The getQAfromAmazon function is an async function, meaning it inherently returns a promise.

However, if you don't return the promise from within that function correctly, you will always receive undefined in the calling code.

The Solution: Returning the Promise

To ensure that your getQAfromAmazon function returns a value properly, you'll want to adjust the structure of the function so that it returns the promise directly instead of returning just after the promise chain. Here’s how you can modify your function:

Updated Function Code

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

Navigation Through the Code Changes

Return Statement: The async function now returns the promise directly with return puppeteer.launch(...), linking the async activity back to the getQAfromAmazon() call.

Error Handling: The catch block provides a way to handle any errors that may occur during the process of launching Puppeteer or fetching data.

Final Thoughts

In JavaScript, handling asynchronous operations accurately is crucial for ensuring your functions return the expected values. By returning the promise correctly from the getQAfromAmazon function, you prevent the situation of getting undefined in your code.

Always remember to test your functions after making changes to ensure everything performs as expected. Now you are equipped with the tools necessary to resolve this specific issue with your async functions in JavaScript!