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Learn how to solve the issue of empty records in CSV writing due to asynchronous calls in JavaScript using the `async-await` pattern combined with promises.
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How to Effectively Handle Asynchronous Operations in JavaScript to Write CSV Files

JavaScript, especially in the context of web scraping and file handling, can sometimes present challenges when managing asynchronous operations. One common issue that developers encounter is the problem of obtaining data from asynchronous functions before the main function resolves and returns an empty array.

In this guide, we will explore a scenario where we need to scrape data, fetch additional information, and then write this enriched data to a CSV file using JavaScript. We will break down the solution into clear sections, making it easy to follow along.

The Problem Explained

The original problem arises when you attempt to scrape data from a CSV file and simultaneously fetch keys from an API based on the scraped data. The expected flow is as follows:

Reading Data: The makeCsv function reads a local CSV file and initiates requests for additional data.

Fetching Keys: The getPubKey function fetches a key against each account name retrieved from the CSV.

Combining Data: makeCsv appends the fetched keys to the existing data.

Final Output: The writeFile function attempts to write the enriched records to a new CSV file.

However, because the getPubKey function returns a promise, makeCsv resolves its promise before all keys are fetched, causing an empty records array.

The Solution: Using Promises to Ensure Data is Fetched

To address the issue of empty records, we need to modify how we handle asynchronous calls in the makeCsv function. Here’s how:

Step 1: Collect Promises

Instead of awaiting the result of getPubKey directly within the piping of the CSV, we will collect promises in an array. Once all promises are collected, we can use Promise.all() to wait for all of them to resolve.

Step 2: Refactor makeCsv

Here’s the updated code for the makeCsv function:

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

Step 3: Remaining Functions Unchanged

The rest of your code remains largely the same. The getPubkey function remains asynchronous and fetches the key adequately.

Complete Working Example

Bringing together all the changes, your complete code will look something like this:

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

Conclusion

By using Promise.all() and collecting all asynchronous calls, we can ensure that all data is fetched before resolving the main promise in makeCsv. This way, our writeFile function receives all the necessary data, and we avoid the pitfall of writing an empty array to the CSV file.

So, the next time you face this challenge in JavaScript, remember to handle your asynchronous logic carefully to achieve the desired outcomes efficiently!