Before you’re able to interact with a file that sits in your filesystem, you must get a file descriptor.

A file descriptor is what’s returned by opening the file using the open() method offered by the fs module:

const fs = require('fs')

fs.open('/Users/flavio/test.txt', 'r', (err, fd) => {
  //fd is our file descriptor
})

Notice the r we used as the second parameter to the fs.open() call.

That flag means we open the file for reading.

Other flags you’ll commonly use are:

• r+ — open for reading and writing
• w+ — open for reading and writing, with the stream at the start; creates the file if it does not exist
• a — open for writing, with the stream at the end; creates the file if it does not exist
• a+ — open for reading and writing, with the stream at the end; creates the file if it does not exist

You can also use fs.openSync(), which returns the file descriptor instead of passing it to a callback:

const fs = require('fs')

try {
  const fd = fs.openSync('/Users/flavio/test.txt', 'r')
} catch (err) {
  console.error(err)
}

Once you get the file descriptor, in whatever way you choose, you can perform all the operations that require it, like reading from or writing to the file.

Lessons in this unit:

0:	Introduction
1:	How to check if a file exists in Node.js
2:	How to create an empty file in Node.js
3:	How to get the names of all the files in a folder in Node
4:	How to get the last updated date of a file using Node.js
5:	How to remove a file with Node.js
6:	How to write a JSON object to file in Node.js
7:	How to empty a folder in Node.js
8:	▶︎ Working with file descriptors in Node
9:	Node File Paths
10:	Node file stats
11:	Working with folders in Node
12:	How to use the Node.js fs module with async/await
13:	How to get the current folder in Node
14:	How to get the file extension in Node.js from the MIME type
15:	How to get the file extension in Node.js
16:	How to list files in a folder in Node
17:	How to mass rename files in Node.js
18:	Node.js get all files in a folder recursively
19:	Incrementing multiple folders numbers at once using Node.js
20:	Save some text to a file in Node.js