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title
| title |
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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
- Append to files
- Delete files
- Rename files
- Move 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.
Append to files
The fs.appendFile() method is used to append text at the end of a file on your computer. It takes three arguments - filename, text to be appended at the end and a call back function.
const fs = require('fs');
fs.appendFile('output.txt', ' This is added at the end.', function (err) {
if (err) {
console.log(err);
}
else {
console.log('Text Appended!');
}
});
The above code adds ' This is added at the end.' at the end of input.txt file on your computer.
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 output.txt.
- Now open your console in the working directory and execute the command
node app.js.
Note : The output.txt file should be present in the same directory where your Node.js code file is present otherwise it will throw an error.
Delete files
The fs.unlink() method is used to files from your computer. It takes two arguments - filename and a call back function.
const fs = require('fs');
fs.unlink('delete_me.txt', function (err) {
if (err) {
console.log(err);
}
else {
console.log('File deleted!');
}
});
The above deletes input.txt file from your computer.
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 delete_me.txt.
- Now open your console in the working directory and execute the command
node app.js.
Note : The file you want to delete should exist otherwise it will throw an error.In this example the delete_me.txt file is in the same directory as the Node.js code file.
Rename files
The fs.rename() method is used to rename a file on your computer. It takes three arguments - filename, name to rename to and a call back function.
const fs = require('fs');
fs.rename('myfile.txt', 'myrenamedfile.txt', function (err) {
if (err) {
console.log(err);
} else {
console.log('File Renamed!');
}
});
The above code will rename myfile.txt file to myrenamedfile.txt.
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 myfile.txt.
- Now open your console in the working directory and execute the command
node app.js.
Note : The myfile.txt file should be present in the same directory where your Node.js code file is present otherwise it will throw an error.
Move files
Moving files is pretty much the same as renaming them.
const fs = require('fs');
fs.rename('myfile.txt', 'copy/myrenamedfile.txt', function (err) {
if (err) {
console.log(err);
} else {
console.log('File Moved!');
}
});
The above code will move myfile.txt file to a directory called copy with the name myrenamedfile.txt.
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 myfile.txt.
- Create a directory named copy
- Now open your console in the working directory and execute the command
node app.js.
Note : The myfile.txt file should be present in the same directory where your Node.js code file is present otherwise it will throw an error. Also the directory you want to copy the file to must exist otherwise it will throw an error