freeCodeCamp/guide/english/nodejs/file-system/index.md

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File System

File System

The Node.js File System module allows you to work with the file system on your computer.

Node.js has a set of built-in modules which you can use without any further installation. Similarly File System module contains a set of functions which are required to perform different operations on files such as read and write operation.

In order to to include a module, use the require() function with the name of the module.

const fs = require('fs');

Common use for the File System module:

• Read files
• Create files
• Update files
• Delete files
• Rename files

Reading a file

The fs.readFile() method is used to read file on your computer. It takes three arguments - filename, encoding and a call back function.

Node.js code to read file from your computer and return the content to the console.

Asynchronous

const fs = require('fs');
fs.readFile('path/to/input.txt', 'utf-8', (err, data) => {
    if (err) throw err;
    console.log("Content present in input.txt file : " + data.toString());
});

Synchronous

const fs = require('fs');
try {
    var data = fs.readFileSync('path/to/input.txt', 'utf-8');
} catch (err){
    console.log(err.message);
}
console.log("Content present in input.txt file: " + data.toString());

The above code reads a file input.txt from your computer and returns the content to the console.

Steps for execution :

• You should have Node.js installed in your computer.
• Create a file app.js and paste the above code.
• Create a file input.txt and write some content into it.
• Now open your console in the working directory and execute the command node app.js.

Note : The input.txt file should be present in the same directory where your Node.js code file is present otherwise it will throw an error.

Writing in a file

The fs.writeFile() method takes three arguments - filename, content and a call back function.

Node.js code to write content into file.

Asynchronous

const fs = require('fs');
fs.writeFile('path/to/output.txt', "New content added", (err) => {
    if (err) throw err;
    console.log("The file is saved");
});

Synchronous

const fs = require('fs');
var data = "New Content Added"
try {
    fs.writeFileSync('path/to/output.txt', data, encoding='utf-8', flag='w')
    console.log("The file us saved")
} catch (err) {
    console.log("The file could not be updated due to: " + err.message);
}

The above code creates a file output.txt and add content New content added to it.

Steps for execution :

• You should have Node.js installed in your computer.
• Create a file app.js and paste the above code.
• Now open your console in the working directory and execute the command node app.js.

Note : If file does not exist then the fs.writeFile() method creates a file and writes the content into it. On the contrary if the file exists then it overwrites the content in the file.

Resources

• Node.js API
• W3 Schools