Скачать или смотреть How to Return Values from an async/await Function Inside Another async/await Function (Puppeteer)

Learn how to effectively return values from asynchronous functions in JavaScript, especially when using Puppeteer. Discover the best practices for handling Promises with async/await.
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This video is based on the question https://stackoverflow.com/q/67564024/ asked by the user 'The Novice' ( https://stackoverflow.com/u/4397297/ ) and on the answer https://stackoverflow.com/a/67564069/ provided by the user 'Nisanth Reddy' ( https://stackoverflow.com/u/10780861/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Return Values from an async/await Function Inside Another async/await Function (Puppeteer)

When working with JavaScript, especially in Node.js applications that utilize Puppeteer for web scraping or browser automation, you might face challenges with asynchronous code execution. In particular, returning values from an async/await function nested inside another async/await function can be confusing.

The Issue: Why Does It Return a Pending Promise?

Take a look at the following code snippet:

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

In this example, when you run the code, instead of seeing "Text on page found" printed to the console, you receive:

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

So, what causes this issue? The reason lies in the fact that puppeteer.launch({ headless: true }) returns a Promise, which essentially allows you to attach the .then() method to handle the resolved value. However, the value returned from the main function is another Promise, and that's why the output remains pending until the nested function is resolved.

Solution 1: Using .then() to Access the Value

One straightforward solution to this problem is to continue using the .then() method to access the result once the promise resolves. You can modify your code like this:

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

With this approach:

You call main, which returns a Promise.

By using .then(value => console.log(value)), you print the actual resolved value instead of the pending promise.

Solution 2: Using async/await Syntax

If you prefer a cleaner and more modern approach, you can use async/await syntax, which allows you to write asynchronous code that looks synchronous. When using this method, make sure you are in an async function context. An example of this method looks like this:

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

In this example, we encapsulate the logfile in another async function called execute.

We then await the main function's execution, which correctly returns the resolved value.

Conclusion

When handling promises in asynchronous JavaScript with Puppeteer, it’s crucial to understand how promises work and the importance of using the right syntax to access their values.

By using either the .then method to access resolved values or employing the more modern async/await syntax, you can effectively manage your asynchronous code without getting stuck on unresolved promises.

Now you're equipped to tackle returning values from async functions within async functions using Puppeteer. Happy coding!