Tutorial on Node File System

iFour ConsultancyNode File System
https://www.ifourtechnolab.com/nodejs-blockchain-software-development

 Node.js gives the functionality of File I/O by providing wrappers around the
standard POSIX functions. In Node.js, File I/O methods can be performed in both
synchronous as well as asynchronous form depending upon the user requirements.
 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');
Introduction

 Common use for the File System module:
1. Read files
2. Write files
3. Append files
4. Delete files
5. Rename files
Use of File System

 Every method in the fs module has synchronous as well as asynchronous forms.
Asynchronous methods take the last parameter as the completion function callback
and the first parameter of the callback function as error. It is better to use an
asynchronous method instead of a synchronous method, as the former never
blocks a program during its execution, whereas the second one does.
Synchronous vs Asynchronous

 Every method in fs module has synchronous and asynchronous forms.
 Asynchronous methods take a last parameter as completion function callback.
Asynchronous method is preferred over synchronous method because it never
blocks the program execution where as the synchronous method blocks.
 Example:
Create File: input.txt
We are reading this file using node.js
Node.js Reading File

 Example: Create File main.js
For Asynchronous read :
var fs = require("fs");
// Asynchronous read
fs.readFile('input.txt', function (err, data) {
if (err) {
return console.error(err);
}
console.log("Asynchronous read: " + data.toString());

For Synchronous read :
var data = fs.readFileSync('input.html');
console.log("Synchronous read: " + data.toString());
console.log("Program Ended");
 Open command prompt and run the main.js:
> node main.js

 Node.js fs.writeFile() function writes data to a file asynchronously with replacing
the file in case of already exists. This function can write data from string or a buffer.
 The encoding option is ignored if data is a buffer. It defaults encoding is ‘utf8’,
Default file mode is 0666 and default flag is used ‘w’ means write mode.
1. path is the filename with path.
2. data is the String or buffer to write
3. options can be an object which is like {encoding, mode, flag}.
4. callback function takes single parameter err and used to return errors.
 Syntax:
fs.writeFile(filename, data[, options], callback)
Node.js Writing a file

 There are two ways for writing a file in nodejs :
For Asynchronous Write :
var content= "this is the content in the file";
fs.writeFile('input.txt', content , (err) => {
if (err)
throw err;
console.log('It's saved!');
});

For Synchronous write :
var content = "We are writing this file synchronously using
node.js";
fs.writeFileSync('input.txt', content);
console.log("File Written Successfully");
> node main.js

 To append data to file in Node.js, use Node FS appendFile() function for
asynchronous file operation or Node FS appendFileSync() function for synchronous
file operation.
filepath is a String that specifies file path
data is what you append to the file
options to specify encoding/mode/flag
 Syntax:
fs.appendFile(filepath, data, options, callback_function);
fs.appendFileSync(filepath, data, options);
Append a File using Nodejs

 There are two ways for Appending a file using nodejs :
For Asynchronous Append :
new_data = "This data will be appended at the end of the file.";
fs.appendFile('input.txt', new_data , (err) => {
if(err)
throw err;
console.log('The new_content was appended successfully');
});

Example: Create File main.js
For Synchronous Append :
var content = "We are Appending this file synchronously using node.js";
fs.appendFileSync('input.txt', content);
console.log("File Appended Successfully");
> node main.js

 To rename file with Node FS, use fs.rename(new_file_name, old_file_name,
callback_function) for asynchronous file rename operation and use
fs.renameSync(new_file_name, old_file_name) for synchronous file rename
operation.
new_file_path : The new file path you would like to assign
old_file_path : Path to the file whose name is to be changed
callback_function : When file renaming operation is done, Callback Function is
called with an error object.
 Syntax:
fs.rename(new_file_path, old_file_path, callback_function)
fs.renameSync(new_file_path, old_file_path)
Rename a File in Nodejs

For Asynchronous Rename :
fs.rename('input.txt', 'newinput.txt', (err) => {
if (err)
throw err;
console.log('File renamed successfully');
});
console.log("This method is Asynchronous");

For Synchronous Rename :
fs.renameSync('input.txt', 'newinput.txt');
console.log('File renamed successfully');
console.log("This method is Synchronous");
> node main.js

 To delete a file in Node.js, Node FS unlink(path, callback) can be used for
asynchronous file operation and unlinkSync(path) can be used for synchronous file
operation.
 Syntax:
fs.unlink(filePath, callbackFunction)
fs.unlinkSync(filePath)
Delete a File in Nodejs

For Asynchronous Delete :
var filename = 'input.txt';
fs.unlink(filename, (err) => {
if (err)
throw err;
console.log('File deleted successfully');
});

For Synchronous Delete:
var filename = 'input.txt';
fs.unlinkSync(filename);
console.log('File Deleted Successfully');
> node main.js

Tutorial on Node File System

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