The Node fs module
The fs module of Node.js provides useful functions to interact with the file system
The fs
module provides a lot of very useful functionality to access and interact with the file system.
There is no need to install it. Being part of the Node core, it can be used by requiring it:
const fs = require('fs')
Once you do so, you have access to all its methods, which include:
fs.access()
: check if the file exists and Node can access it with its permissionsfs.appendFile()
: append data to a file. If the file does not exist, it’s createdfs.chmod()
: change the permissions of a file specified by the filename passed. Related:fs.lchmod()
,fs.fchmod()
fs.chown()
: change the owner and group of a file specified by the filename passed. Related:fs.fchown()
,fs.lchown()
fs.close()
: close a file descriptorfs.copyFile()
: copies a filefs.createReadStream()
: create a readable file streamfs.createWriteStream()
: create a writable file streamfs.link()
: create a new hard link to a filefs.mkdir()
: create a new folderfs.mkdtemp()
: create a temporary directoryfs.open()
: set the file modefs.readdir()
: read the contents of a directoryfs.readFile()
: read the content of a file. Related:fs.read()
fs.readlink()
: read the value of a symbolic linkfs.realpath()
: resolve relative file path pointers (.
,..
) to the full pathfs.rename()
: rename a file or folderfs.rmdir()
: remove a folderfs.stat()
: returns the status of the file identified by the filename passed. Related:fs.fstat()
,fs.lstat()
fs.symlink()
: create a new symbolic link to a filefs.truncate()
: truncate to the specified length the file identified by the filename passed. Related:fs.ftruncate()
fs.unlink()
: remove a file or a symbolic linkfs.unwatchFile()
: stop watching for changes on a filefs.utimes()
: change the timestamp of the file identified by the filename passed. Related:fs.futimes()
fs.watchFile()
: start watching for changes on a file. Related:fs.watch()
fs.writeFile()
: write data to a file. Related:fs.write()
One peculiar thing about the fs
module is that all the methods are asynchronous by default, but they can also work synchronously by appending Sync
.
For example:
fs.rename()
fs.renameSync()
fs.write()
fs.writeSync()
This makes a huge difference in your application flow.
Node 10 includes experimental support for a promise based API
For example let’s examine the fs.rename()
method. The asynchronous API is used with a callback:
const fs = require('fs')
fs.rename('before.json', 'after.json', (err) => {
if (err) {
return console.error(err)
}
//done
})
A synchronous API can be used like this, with a try/catch block to handle errors:
const fs = require('fs')
try {
fs.renameSync('before.json', 'after.json')
//done
} catch (err) {
console.error(err)
}
The key difference here is that the execution of your script will block in the second example, until the file operation succeeded.
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