The fs module is a core module provided by Node.js itself, not available by default in JavaScript. This module plays a crucial role in interacting with the file system, allowing developers to perform various file-related operations such as reading, writing, appending, deleting, and more.

Writing to a File

1. fs.writeFileSync("./created.txt", "Created file using writeFileSync");

   • This line uses the synchronous version of the writeFile function called writeFileSync, to write data to a file named "created.txt".

   • The first parameter is the file path, which in this case is "./created.txt" (relative path).

   • The second parameter is the data you want to write to the file, which is the string "Created file using writeFileSync".

2. fs.writeFile("./created.txt", "Created file using writeFile", (err) => { ... });

   • This line uses the asynchronous version of the writeFile function, called writeFile, to write data to a file named "created.txt".

   • Similarly, the first parameter is the file path.

   • The second parameter is the data to be written.

   • The third parameter is a callback function that is invoked after the write operation is completed or if an error occurs

Thus for every method provide we have either Async or Sync way to do the operation, when it is synchronous then it doesn't require a callback function. I wrote another blog that specifies Blocking vs Non-Blocking execution which is very important from an interview perspective and application-wise.

Reading from a File

1. const result = fs.readFileSync("./created.txt", "utf-8");

   • These lines read the contents of the file "created.txt" synchronously using the readFileSync function.

   • The first parameter is the file path.

   • The second parameter is the encoding, which is set to "utf-8" to read the file as a text file.

   • The result is stored in the result variable, and it is logged to the console.

Some alternative encodings include ASCII (for basic English characters), UTF-16 (uses 2 bytes per character), and ISO-8859-1 (also known as Latin-1).

In many cases, UTF-8 is a good choice because of its compatibility and support for a wide range of characters.

1. fs.readFile("./created.txt", "utf-8", (err, result) => { ... });

   • These lines read the contents of the file "created.txt" asynchronously using the readFile function.

   • The first two parameters are the file path and the encoding, similar to the readFileSync function.

   • The third parameter is a callback function that is invoked with two arguments: an error (if any) and the file contents.

Appending to a File

1. fs.appendFileSync("./log.txt", "Data logged appended \n");

   • This line demonstrates how to append data to a file using the appendFileSync function.

   • The first parameter is the file path.

   • The second parameter is the data to be appended to the file.

One common use case of appendFileSync is creating and maintaining a log file that stores a chronological record of events and logs. This log file can be useful for debugging, error tracking, or general auditing purposes. Here's an example scenario to illustrate this use case:

Copying a File

1. fs.copyFileSync("./created.txt", "./copy.txt");

   • This line copies the contents of "created.txt" to "copy.txt" using the copyFileSync function.

   • The first parameter is the source file path, and the second parameter is the destination file path.

Conclusion

In this article, we explored the basics of file streams in Node.js using the fs module. We covered how to write to a file, read from a file, append data to a file, and copy a file. By utilizing these file stream operations, you can efficiently handle file I/O tasks in your Node.js applications.

Please note that when working with file streams, it's important to handle errors appropriately and close the streams after use to prevent resource leaks. Additionally, the asynchronous functions are generally preferred in Node.js applications to ensure non-blocking behavior.

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