Solving Promise Inside a Loop in Async Functions with Firebase and Redux

Описание: A guide to handling promises correctly in async functions when working with Firebase and Redux. Learn how to replace user IDs with actual user information efficiently.
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This video is based on the question https://stackoverflow.com/q/62735251/ asked by the user 'scripter' ( https://stackoverflow.com/u/10170117/ ) and on the answer https://stackoverflow.com/a/62735356/ provided by the user 'andresmijares' ( https://stackoverflow.com/u/607477/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Problem

If you’re working on a React project with Firebase and Redux, you may encounter a common issue when dealing with promises inside loops, particularly when modifying data fetched from your database. For instance, you might want to replace user IDs stored in various items with their respective user information. This challenge often leads to encountering an empty array, which signifies that the modifications didn’t resolve as expected before returning results.

In this guide, we'll explore a solution to this problem, focusing on how to properly handle promises in your asynchronous functions.

The Original Code

Here’s a snippet of the code that poses problems due to improper handling of asynchronous operations:

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

The core issue lies in the use of forEach combined with asynchronous calls, leading to the items array being returned before it’s populated.

The Solution: Using for...of Loop

To effectively handle promises inside a loop, we can switch from forEach to a for...of loop in conjunction with the await keyword. This ensures that each promise resolves before moving on to the next item. Here’s a reorganized solution:

Revised Code

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

Key Changes Explained

Utilizing for...of: By using the for...of loop, we can easily iterate through the items and await the resolution of each promise before proceeding to the next iteration. This keeps the operations well-ordered and ensures that the modified data is ready for return.

Awaiting User Data Retrieval: Each retrieval of user data happens after awaiting the previous retrieval, which prevents races and ensures all users’ data is populated correctly.

Removing Nested Promises: The code is cleaner and easier to read because we eliminated nested promise chains, making it straightforward to follow the flow of data.

Conclusion

Dealing with promises inside loops can seem daunting, especially when working with complex data structures, such as those from Firebase. However, by adopting a more structured approach with for...of and await, you can make your code easier to read and more reliable.

If you find yourself struggling with asynchronous operations, remember this pattern, and you’ll be well-equipped to tackle similar challenges in your projects. Happy coding!