FAQ: Node.js Essentials - The FS Module

This community-built FAQ covers the “The FS Module” exercise from the lesson “Node.js Essentials”.

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Learn Node.js

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So I was hoping to grep certain part of the file with fs
However, it seems like it’s not possible to return value or reassign global variable in the callback
Is there any way this could be done? or perhaps reasons why it shouldnt be done?

const fs = require('fs');
var secretWord = "empty"

fs.readFile("finalFile.txt", 'utf-8', (err, data) => {
    module.exports.secretWord = data.substr(data.indexOf(`"`)+1, data.lastIndexOf(`"`)-data.indexOf(`"`)-1);

You can try readFileSync()


const fs = require(‘fs’);

let getData = async () =>{

let secretWord = await ‘./finalFile.txt’

fs.readFile(secretWord, ‘utf-8’, (err, data) =>{

if (err){








It doesn’t take it as correct solution.

you have to read the data of the final file and assign the word you read to the secretWord like this secretWord = 'the actual word'

1 Like

For the callback function, I’m still not sure how the fs.readFile() knows how to pass the contents of ‘/.file.txt’ as the second argument. The callback function has two arguments, and even though its arguments are labeled as err and data, those could have been labeled anything. How does fs.readFile() know to pass a both a null or “falsy value” as the first argument and the data as the second argument (assuming there are no errors)?

I think I figured it out… Looking at the documentation for fs.filestream() on Node.

The fs.filestream() method is built specifically for callback functions with arguments (err, data). That makes sense, but wasn’t clear based on the lesson content. Good to know.