how to save file after writing nodejs code example

Example 1: data not write in file node js

const fs = require('fs');

fs.readFile('file.txt', 'utf-8', (err, data) => {
    if(err) {
        throw err;
    }
    console.log(data);
});

Example 2: how to write to a file with javascript without nodejs

function convertToJSON() {
  var firstname = document.getElementById('firstname').value;
  var lastname = document.getElementById('lastname').value;
  var email = document.getElementById('email').value;

  var jsonObject = {
    "FirstName": firstname,
    "LastName": lastname,
    "email": email
  }

  document.getElementById('output').value = JSON.stringify(jsonObject)
}

function saveToFile() {
  convertToJSON();
  var jsonObjectAsString = document.getElementById('output').value;

  var blob = new Blob([jsonObjectAsString], {
    //type: 'application/json'
    type: 'octet/stream'
  });
  console.log(blob);

  var anchor = document.createElement('a')
  anchor.download = "user.json";
  anchor.href = window.URL.createObjectURL(blob);
  anchor.innerHTML = "download"
  anchor.click();

  console.log(anchor);

  document.getElementById('output').append(anchor)


}