Скачать или смотреть How to Use async/await with fs.readFile in Node.js

Learn how to handle file reading asynchronously in Node.js using `async/await` and improve your coding skills.
---
This video is based on the question https://stackoverflow.com/q/65986153/ asked by the user 'Steve' ( https://stackoverflow.com/u/4971859/ ) and on the answer https://stackoverflow.com/a/65986425/ provided by the user 'jfriend00' ( https://stackoverflow.com/u/816620/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: How to make fs.readFile async await?

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
How to Use async/await with fs.readFile in Node.js

In Node.js, working with files can sometimes lead to confusion, especially when trying to manage asynchronous file operations effectively. A common issue arises when using the fs.readFile method. If you find yourself needing to read files in a directory and you want to process each file immediately after reading it (rather than logging all filenames first), using async/await can help simplify your code. In this post, we’ll walk through how to effectively implement async/await for reading files within a directory.

The Problem

Imagine you have a Node.js function that reads all files in a directory, but you encounter a problem. With your current implementation, the filenames are printed first, and then the content is read, which is not the expected behavior. You want to read each file's content right after logging its name. How can you achieve this?

Here’s a snippet of your initial code that causes this issue:

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

Understanding the Issue

The key issue here is that:

You are using Array.prototype.map() which runs the function on each file in parallel. Thus, it triggers all reads at once, leading to the printing of all filenames before their contents.

The fs.readFile function is asynchronous and uses a callback, which does not work seamlessly with async/await unless you use its promise-based counterpart.

The Solution

To effectively read files one by one and ensure that the content of each file is processed immediately after logging its name, you can follow these steps:

Step 1: Use Promises

Utilize the promise versions of the fs functions by accessing fs.promises. This will allow you to use await effectively.

Step 2: Replace map() with for...of Loop

Replace the map() function with a for...of loop. This will ensure that each iteration waits for the previous one to complete before proceeding.

Step 3: Write the Code

Here’s how the corrected code looks:

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

Important Points to Note

Sequential vs Parallel Execution: Using for...of ensures sequential execution whereas .map() allows for parallel execution. Choose based on your needs.

Error Handling: Make sure to handle any potential errors when reading files, which is essential for robust code.

Async Functions: Remember that functions using await must be declared as async, which is vital for the code to work correctly.

Conclusion

Using async/await in Node.js can greatly enhance the readability and management of your code, especially when working with asynchronous file operations. By converting callback-based functions to promises and restructuring your looping logic, you can ensure that your files are read in the order you desire. Armed with this knowledge, you're now ready to handle file reading in a more elegant and controlled manner. Happy coding!