Node fs.appendFile() Function
The fs.appendFile() method is used to asynchronously append the given data to a file. A new file is created if it does not exist. The options parameter can be used to modify the behavior of the operation.
Syntax:
fs.appendFile( path, data[, options], callback )
Parameters:
This method accepts four parameters as mentioned above and described below:
- path: It is a String, Buffer, URL or number that denotes the source filename or file descriptor that will be appended to.
- data: It is a String or Buffer that denotes the data that has to be appended.
- options: It is an string or an object that can be used to specify optional parameters that will affect the output. It has three optional parameters:
- encoding: It is a string which specifies the encoding of the file. The default value is ‘utf8’.
- mode: It is an integer which specifies the file mode. The default value is ‘0o666’.
- flag: It is a string which specifies the flag used while appending to the file. The default value is ‘a’.
- callback: It is a function that would be called when the method is executed.
- err: It is an error that would be thrown if the method fails.
Below examples illustrate the fs.appendFile() method in Node.js:
Example 1: This example shows the appending of the given text to a file.
Javascript
// Node.js program to demonstrate the // fs.appendFile() method // Import the filesystem module const fs = require('fs');// Get the file contents before the append operation console.log("\nFile Contents of file before append:", fs.readFileSync("example_file.txt", "utf8"));fs.appendFile("example_file.txt", "World", (err) => { if (err) { console.log(err); } else { // Get the file contents after the append operation console.log("\nFile Contents of file after append:", fs.readFileSync("example_file.txt", "utf8")); }}); |
Output:
File Contents of file before append: Hello
File Contents of file after append: HelloWorld
Example 2: This example shows the usage of the optional parameters to change the file encoding, mode, and flag of the operation.
Javascript
// Node.js program to demonstrate the // fs.appendFile() method // Import the filesystem module const fs = require('fs');// Get the file contents before the append operation console.log("\nFile Contents of file before append:", fs.readFileSync("example_file.txt", "utf8"));fs.appendFile("example_file.txt", " - w3wiki", { encoding: "latin1", mode: 0o666, flag: "a" }, (err) => { if (err) { console.log(err); } else { // Get the file contents after the append operation console.log("\nFile Contents of file after append:", fs.readFileSync("example_file.txt", "utf8")); } }); |
Output:
File Contents of file before append: This is a test file
File Contents of file after append: This is a test file - BeginnerForGeek
We have a Cheat Sheet on Node fs modules where we covered all the fs methods to check those please go through Node File System Complete Reference article