node.js: fs.appendFile(path, data[, options], callback): Append data to a file synchronously

fs.appendFile(path, data[, options], callback)This method appends data to a file synchronously. Below table summarizes the arguments of appendFile method.

Argument	Type	Description
path	string or Buffer or URL or number	Specifies the file name or file descriptor.
data	string or Buffer	Data to be appended to a file
options	string or Object	Below table summarizes the options supported by appendFile method. Option Type Description encoding String Default value is utf8 mode integer Default: 0o666 flag string Default: 'a'. 'a' - Open file for appending. The file is created if it does not exist. 'ax' - Like 'a' but fails if the path exists. 'a+' - Open file for reading and appending. The file is created if it does not exist. 'ax+' - Like 'a+' but fails if the path exists. 'as' - Open file for appending in synchronous mode. The file is created if it does not exist. 'as+' - Open file for reading and appending in synchronous mode. The file is created if it does not exist. 'r' - Open file for reading. An exception occurs if the file does not exist. 'r+' - Open file for reading and writing. An exception occurs if the file does not exist. 'rs+' - Open file for reading and writing in synchronous mode. Instructs the operating system to bypass the local file system cache. 'w' - Open file for writing. The file is created (if it does not exist) or truncated (if it exists). 'wx' - Like 'w' but fails if the path exists. 'w+' - Open file for reading and writing. The file is created (if it does not exist) or truncated (if it exists). 'wx+' - Like 'w+' but fails if the path exists.
callback	Function	This function is called, when the data is appended to the file. This function takes ‘err’ as an argument. If any error occurs while appending the content, ‘err’ is populated with error information.

Below table summarizes the modes supported by node.js

Constant (mode)	Octal value	Description
fs.constants.S_IRUSR	0o400	read by owner
fs.constants.S_IWUSR	0o200	write by owner
fs.constants.S_IXUSR	0o100	execute/search by owner
fs.constants.S_IRGRP	0o40	read by group
fs.constants.S_IWGRP	0o20	write by group
fs.constants.S_IXGRP	0o10	execute/search by group
fs.constants.S_IROTH	0o4	read by others
fs.constants.S_IWOTH	0o2	write by others
fs.constants.S_IXOTH	0o1	execute/search by others

        

Find the below working application.

HelloWorld.js

var fs = require('fs');

var filePath = 'out.txt';

var msg1 = 'Hello, How are you\n';
var msg2 = 'I am fine, How are you?\n';
var msg3 = 'I am fine too, thank you!!!!!\n';

fs.appendFile(filePath, msg1, (err) => {
    if (err) {
        console.log('error occured while appending %s', msg1);
    }

});

fs.appendFile(filePath, msg2, (err) => {
    if (err) {
        console.log('error occured while appending %s', msg1);
    }
});

fs.appendFile(filePath, msg3, (err) => {
    if (err) {
        console.log('error occured while appending %s', msg1);
    }
});

Open ‘out.txt’, you can see below messages.

I am fine, How are you?

I am fine too, thank you!!!!!

Hello, How are you

I am fine too, thank you!!!!!

I am fine, How are you?

Hello, How are you

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