Reading a file in Node.js

Node.js / September 2, 2022 / TopCode / 0

Introduction

Reading a file into memory is a very common programming task. If you are building an application, then one of the important things is to read the content of a file. Node.js core API provides methods to make it easier for us. Node.js fs module provides API to do file operations.

One simplest way to read file is with fs.readFile() as following.

const fs = require('fs')

fs.readFile('/etc/hosts', (err, data) => {
  if (err) {
    console.error(err)
    return
  }
  console.log(data)
})

The above code snippet uses asynchronous API to read the content of the file. Alternatively, you can use the synchronous version fs.readFileSync() as follows.

const fs = require('fs')

try {
  const data = fs.readFileSync('/etc/hosts', 'utf8')
  console.log(data)
} catch (err) {
  console.error(err)
}

Both fs.readFile() and fs.readFileSync() read the full content of the file in memory before returning the data.

Do not use synchronous API fs.readFileSync(). Synchronous API always blocks the Node event loop. As Node.js runs in a single threaded environment. It is advisable to use asynchronous APIs in production environment.

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