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In this short article, we will learn how to read files in Node.js.

Reading Files in Node.js

fsThe module provides many useful functions to access and interact with the file system. fsOne special feature of the module is that all methods are asynchronous by default, but can also be made to work synchronously by adding sync.

We will use fs.readFile()to read the file in Node.js. You need to pass the file path, encoding, and a callback function to call with the file data or error.

fs.readFile()method is a built-in method for reading files. It reads the entire file into a buffer. require()method is used to load modules, such as const fs = require('fs').

grammar:

fs.readFile( filename, encoding, callbackFn )

This method accepts three parameters.

It returns the content, data stored in the file or error encountered while reading the file. Let us understand it with an example.

Code:

const fs = require('fs');
fs.readFile('/helloworld.txt', 'utf8', (err, data) => {
  if (err) {
    console.error(err);
    return;
  }
  console.log(data);
});

The output is as follows:

Hello jiyik.com readers!

Another option is to use the synchronous version fs.readFileSync().

Code:

const fs = require('fs');
try {
  const fileContent = fs.readFileSync('/helloworld.txt', 'utf8');
  console.log(fileContent);
} catch (err) {
  console.error(err);
}

The output is as follows:

Hello jiyik.com readers!

We can also use the method provided by the fs/promises module fsPromises.readFile().

Code:

const fsPromises = require('fs/promises');

async function FileReadFn() {
  try {
    const fileContent = await fsPromises.readFile('/helloworld.txt', { encoding: 'utf8' });
    console.log(fileContent);
  } catch (err) {
    console.log(err);
  }
}
FileReadFn();

The output is as follows:

Hello jiyik.com readers!

fs.readFile()fsPromises.readFile()All fs.readFileSync()three methods read the entire contents of the file into memory before returning the data. This means that large files will greatly affect memory usage and program execution speed .

Rather than waiting for the file to finish reading, we start streaming to the HTTP client as soon as the data is ready to be sent. Streams essentially offer two major advantages over using other methods of data processing.

1. Memory efficiency – You don’t have to load large amounts of data into memory before processing.
2. Time efficiency - It takes much less time to start processing data because you can start processing immediately instead of waiting until the entire payload is available.

On the file stream, call pipe()the method, which takes the source and directs it to the destination. The destination stream is pipe()the return value of the method, which is a very convenient thing that allows us to pipe()chain together multiple calls to .

Code:

const fs = require('fs');
const http = require('http');

const nodeServer = http.createServer((req, res) => {
  const fileStream = fs.createReadStream(`${__dirname}/helloworld.txt`);
  fileStream.pipe(res);
});
nodeServer.listen(3000);

The output is as follows:

Hello jiyik.com readers!