How to Read Files in Nodejs with examples


How to Read Files in Nodejs with examples

By bangarsanju12

In todays world of the most common code to write in any programming language is to work on file handling like reading and writing to a file .

In Nodejs reading a file becomes tricky at times .In this tutorial we are going to Read files in Nodejs code with few common problems and examples that we face day to day .

There are various ways to handle file read in Nodejs , which are .

  1. Sychronus or Blocking
  2. Asynchronus or Non Blocking
  3. Reading all Contents At one
  4. Streaming File Contents.

Read a File Line By Line

The reason I consider this as a simple way is because of the complexity of the method , its pretty simple and any beginner can also start doing this .

Lets understand using code snippet how we can do this .

const fs = require('fs')

fs.readFile('/opt/ctier/names.txt', 'utf8' , (err, data) => {
  if (err) {

We have used fs.readFile() method, passing the file path as parameter, and passed a callback function that will be called with the file data to read . The data argument will have the actual contents of the file and err argument will return if any error occurred while reading the file .

Note :- Utf8 argument is necessary here , in case you do not specify the UTF* parameter this will return a Buffer Object . This was a non blocking way to read a file . Lets understand the blocking way .

var fs = require('fs');

try {
    var data = fs.readFileSync('/opt/ctier/name.txt', 'utf8');
} catch(e) {
    console.log('Error Occurred:', e.stack);

This method can be used where we need to read file synchronized way . It is more of a blocking call in your code hence you need a try... and catch...

Streaming files using fs.createReadStream

Now fs.createReadStream opens a readable stream to read any kind of file . If you are looking to read a file from a specific URL or looking to stream large files of 400MB we can use fs.createReadStream .

fs.createReadStream can read files from URL or from a string . We can also read files from a buffer using fs.createReadStream . Lets look at practical example of using fs.createReadStream .

const fs = require('fs');
const server = require('http').createServer();

server.on('request', (req, res) => {
    const src = fs.createReadStream('/opt/movie.mp4');
    src.on('error', function (error) {
        res.writeHead(404, 'Not Found');

One of the important aspect to check in above line of code is we are using pipe to push the data in res object which is also a kind of eventEmitter . All streams in node are instances of EventEmitter hence we are able to pass that to the response .

Now there are numerous reason why should we prefer streams , here are few important ones .

  • Memory Usage – Apart from normal way of reading files , reading files using streams are way beneficial in terms of memory usage . Memory usage of streams are way lower than non stream way . Have a look at memory comparison here .
  • Time Efficient – It generally takes less time for sending response as streams doesn’t wait for entire file to load and send the response . It sends responses in chunks .

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