Node.js File System Module
Node.js as a File Server
The Node.js file system module allows you to work with the file system on your computer.
To include the File System module, use the require() method:
var fs = require('fs');
Common use for the File System module:
- Read files
- Create files
- Update files
- Delete files
- Rename files
Read Files
The fs.readFile() method is used to read files on your computer.
Assume we have the following HTML file (located in the same folder as Node.js):
demofile1.html
<html>
<body>
<h1>My Header</h1>
<p>My paragraph.</p>
</body>
</html>
Create a Node.js file that reads the HTML file, and return the content:
Example
var http = require('http');
var fs = require('fs');
http.createServer(function (req, res) {
fs.readFile('demofile1.html', function(err, data) {
res.writeHead(200, {'Content-Type': 'text/html'});
res.write(data);
return res.end();
});
}).listen(8080);
Save the code above in a file called “demo_readfile.js”, and initiate the file:
Initiate demo_readfile.js:
C:\Users\Your Name>node demo_readfile.js
If you have followed the same steps on your computer, you will see the same result as the example: http://localhost:8080
Create Files
The File System module has methods for creating new files:
fs.appendFile()fs.open()fs.writeFile()
The fs.appendFile() method appends specified content to a file. If the file does not exist, the file will be created:
Example
Create a new file using the appendFile() method:
var fs = require('fs');
fs.appendFile('mynewfile1.txt', 'Hello content!', function (err) {
if (err) throw err;
console.log('Saved!');
});
The fs.open() method takes a “flag” as the second argument, if the flag is “w” for “writing”, the specified file is opened for writing. If the file does not exist, an empty file is created:
Example
Create a new, empty file using the open() method:
var fs = require('fs');
fs.open('mynewfile2.txt', 'w', function (err, file) {
if (err) throw err;
console.log('Saved!');
});
The fs.writeFile() method replaces the specified file and content if it exists. If the file does not exist, a new file, containing the specified content, will be created:
Example
Create a new file using the writeFile() method:
var fs = require('fs');
fs.writeFile('mynewfile3.txt', 'Hello content!', function (err) {
if (err) throw err;
console.log('Saved!');
});
Update Files
The File System module has methods for updating files:
fs.appendFile()fs.writeFile()
The fs.appendFile() method appends the specified content at the end of the specified file:
Example
Append “This is my text.” to the end of the file “mynewfile1.txt”:
var fs = require('fs');
fs.appendFile('mynewfile1.txt', ' This is my text.', function (err) {
if (err) throw err;
console.log('Updated!');
});
The fs.writeFile() method replaces the specified file and content:
Example
Replace the content of the file “mynewfile3.txt”:
var fs = require('fs');
fs.writeFile('mynewfile3.txt', 'This is my text', function (err) {
if (err) throw err;
console.log('Replaced!');
});
Delete Files
To delete a file with the File System module, use the fs.unlink() method.
The fs.unlink() method deletes the specified file:
Example
Delete “mynewfile2.txt”:
var fs = require('fs');
fs.unlink('mynewfile2.txt', function (err) {
if (err) throw err;
console.log('File deleted!');
});
Rename Files
To rename a file with the File System module, use the fs.rename() method.
The fs.rename() method renames the specified file:
Example
Rename “mynewfile1.txt” to “myrenamedfile.txt”:
var fs = require('fs');
fs.rename('mynewfile1.txt', 'myrenamedfile.txt', function (err) {
if (err) throw err;
console.log('File Renamed!');
});
Upload Files
The Formidable Module
There is a very good module for working with file uploads, called “Formidable”.
The Formidable module can be downloaded and installed using NPM:
C:\Users\Your Name>npm install formidable
After you have downloaded the Formidable module, you can include the module in any application:
var formidable = require('formidable');
Upload Files
Now you are ready to make a web page in Node.js that lets the user upload files to your computer:
Step 1: Create an Upload Form
Create a Node.js file that writes an HTML form, with an upload field:
Example
This code will produce an HTML form:
var http = require('http');
http.createServer(function (req, res) {
res.writeHead(200, {'Content-Type': 'text/html'});
res.write('<form action="fileupload" method="post" enctype="multipart/form-data">');
res.write('<input type="file" name="filetoupload"><br>');
res.write('<input type="submit">');
res.write('</form>');
return res.end();
}).listen(8080);
Step 2: Parse the Uploaded File
Include the Formidable module to be able to parse the uploaded file once it reaches the server.
When the file is uploaded and parsed, it gets placed on a temporary folder on your computer.
Example
The file will be uploaded, and placed on a temporary folder:
var http = require('http');
var formidable = require('formidable');
http.createServer(function (req, res) {
if (req.url == '/fileupload') {
var form = new formidable.IncomingForm();
form.parse(req, function (err, fields, files) {
res.write('File uploaded');
res.end();
});
} else {
res.writeHead(200, {'Content-Type': 'text/html'});
res.write('<form action="fileupload" method="post" enctype="multipart/form-data">');
res.write('<input type="file" name="filetoupload"><br>');
res.write('<input type="submit">');
res.write('</form>');
return res.end();
}
}).listen(8080);
Step 3: Save the File
When a file is successfully uploaded to the server, it is placed on a temporary folder.
The path to this directory can be found in the “files” object, passed as the third argument in the parse() method’s callback function.
To move the file to the folder of your choice, use the File System module, and rename the file:
Example
Include the fs module, and move the file to the current folder:
var http = require('http');
var formidable = require('formidable');
var fs = require('fs');
http.createServer(function (req, res) {
if (req.url == '/fileupload') {
var form = new formidable.IncomingForm();
form.parse(req, function (err, fields, files) {
var oldpath = files.filetoupload.path;
var newpath = 'C:/Users/Your Name/' + files.filetoupload.name;
fs.rename(oldpath, newpath, function (err) {
if (err) throw err;
res.write('File uploaded and moved!');
res.end();
});
});
} else {
res.writeHead(200, {'Content-Type': 'text/html'});
res.write('<form action="fileupload" method="post" enctype="multipart/form-data">');
res.write('<input type="file" name="filetoupload"><br>');
res.write('<input type="submit">');
res.write('</form>');
return res.end();
}
}).listen(8080);
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