Node.js fs.writeFile() Method

The fs.writeFile() method is used to asynchronously write the specified data to a file. By default, the file would be replaced if it exists. The ‘options’ parameter can be used to modify the functionality of the method.

Syntax:

fs.writeFile( file, data, options, callback )

Parameters: This method accept four parameters as mentioned above and described below:

• file: It is a string, Buffer, URL or file description integer that denotes the path of the file where it has to be written. Using a file descriptor will make it behave similar to fs.write() method.
• data: It is a string, Buffer, TypedArray or DataView that will be written to the file.
• options: It is an string or object that can be used to specify optional parameters that will affect the output. It has three optional parameter:
  • encoding: It is a string value that specifies the encoding of the file. The default value is ‘utf8’.
  • mode: It is an integer value that specifies the file mode. The default value is 0o666.
  • flag: It is a string value that specifies the flag used while writing to the file. The default value is ‘w’.
• callback: It is the function that would be called when the method is executed.
  • err: It is an error that would be thrown if the operation fails.

Below examples illustrate the fs.writeFile() method in Node.js:

Example 1:

// Node.js program to demonstrate the
// fs.writeFile() method

// Import the filesystem module
const fs = require('fs');

let data = "This is a file containing a collection of books.";

fs.writeFile("books.txt", data, (err) => {
  if (err)
    console.log(err);
  else {
    console.log("File written successfully\n");
    console.log("The written has the following contents:");
    console.log(fs.readFileSync("books.txt", "utf8"));
  }
});

Output:

File written successfully

The written has the following contents:
This is a file containing a collection of books.

Example 2:

// Node.js program to demonstrate the
// fs.writeFile() method

// Import the filesystem module
const fs = require('fs');

let data = "This is a file containing a collection of movies.";

fs.writeFile("movies.txt", data,
  {
    encoding: "utf8",
    flag: "w",
    mode: 0o666
  },
  (err) => {
    if (err)
      console.log(err);
    else {
      console.log("File written successfully\n");
      console.log("The written has the following contents:");
      console.log(fs.readFileSync("movies.txt", "utf8"));
    }
});

Output:

File written successfully

The written has the following contents:
This is a file containing a collection of movies.

Reference: https://nodejs.org/api/fs.html#fs_fs_writefile_file_data_options_callback