How to read last N bytes of file using NodeJs

Node.Js is a great framework to build I/O applications where there are too many database interactions. Sometimes we need to read bytes of files using Node.Js. In this post, we will cover how to read last n bytes of file using node.js.

Step 1

Create a file named app.js and require fs module in the file.

var fs = require('fs');

Step 2

Use fs.stat to get the file size.

fs.stat('test.txt', function(err, stats) {
  // file size info goes here
  var fileSize = stats.size;
  var bytesToRead = 10; /* <--- Here is the number N. It will read the last 10 bytes of the file */
  var position = fileSize - bytesToRead;  /* <--- Specify the position from where you want to read the file */
});

Step 3

Open and read the file using fs.open and fs.read with file size, position etc values.

fs.open('test.txt', 'r', function(errOpen, fd) {
  fs.read(fd, Buffer.alloc(bytesToRead), 0, bytesToRead, pos, function(errRead, bytesRead, buffer) {
    console.log(buffer.toString('utf8'));
  });
});

Step 4

The complete code goes here-

var fs=require('fs');

fs.stat('test.txt', function(err, stats) {
 const fileSize = stats.size;
 const bytesToRead = 10; 
 const position = fileSize - bytesToRead;   
  fs.open('test.txt', 'r', function(errOpen, fd) {
    fs.read(fd, Buffer.alloc(bytesToRead), 0, bytesToRead, position, function(errRead, bytesRead, buffer) {
      console.log(buffer.toString('utf8'));
    });
  });
});

Here are the contents of my test file-

Result after reading last 10 bytes-

Share your issues/concerns if you get any while reading the bytes of file.

Thanks