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Node JS fs.readFile() Method - GeeksforGeeks

Last Updated : 12 Jul, 2025

​In Node.js, the fs.readFile() method is a fundamental tool for reading files asynchronously, allowing your application to remain responsive while accessing file data. This method is part of Node.js's File System (fs) module, which provides an API for interacting with the file system.

fs.readFile(path, options, callback);

The method accepts three parameters as mentioned above and described below:  

• path: The path to the file to be read. This can be a relative or absolute path.​
• options: An optional object or string that specifies the encoding, file mode, and flag. If not provided, the default encoding is 'utf8'.​
• callback: A function that is called after the file has been read. It takes two arguments:​
  • err: An error object if an error occurred, or null if no error.​
  • data: The contents of the file. If no encoding is specified, this will be a Buffer object; otherwise, it will be a string

Return Value:

The method does not return a value. Instead, it invokes the provided callback function with the file's contents or an error.

​In Node.js, there are two primary methods for reading files: fs.readFile() and fs.readFileSync(). Understanding the differences between them is essential for effective file handling in your applications.

There are two methods of Aysno and sync lets compare both of them in befiried:

• fs.readFile(): Asynchronously reads files, allowing other operations to continue while the file is being read.
• fs.readFileSync(): Synchronously reads files, blocking the event loop until the operation completes.

For non-blocking behavior, fs.readFile() is preferred.

To use fs.readFile() in your Node.js application, follow these steps:

Open your terminal and create a new directory for your project:

mkdir folder-name
cd folder-name

Initialize a new Node.js project:

npm init -y

Create an index.js file:

touch index.js

In index.js, add the following code to read a file asynchronously:

const fs = require('fs');

fs.readFile('example.txt', 'utf8', (err, data) => {
  if (err) {
    console.error('Error reading file:', err);
    return;
  }
  console.log('File contents:', data);
});

Ensure you have a file named example.txt in your project directory. Then, run your application:

node index.js

If example.txt contains text, it will be displayed in the console.

Proper error handling is crucial when working with file operations. The callback function's err parameter will contain error information if an error occurs. For example:

fs.readFile('nonexistent.txt', 'utf8', (err, data) => {
  if (err) {
    console.error('Error reading file:', err);
    return;
  }
  console.log('File contents:', data);
});

If nonexistent.txt does not exist, the error will be logged.

• Always Handle Errors: Ensure your callback functions handle errors to prevent application crashes.
• Use Appropriate Encoding: Specify the correct encoding to receive data as a string. For binary data, omit the encoding.
• Consider File Size: For large files, consider using streams to read the file in chunks, preventing high memory usage.

The fs.readFile() method is a powerful tool for asynchronous file reading in Node.js, contributing to efficient and non-blocking applications. By understanding its usage, syntax, and best practices, you can effectively manage file operations in your projects.

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