how to write to a file with javascript without nodejs

                                    // fs_write.js

const fs = require('fs');

// specify the path to the file, and create a buffer with characters we want to write
let path = 'ghetto_gospel.txt';
let buffer = new Buffer('Those who wish to follow me\nI welcome with my hands\nAnd the red sun sinks at last');

// open the file in writing mode, adding a callback function where we do the actual writing
fs.open(path, 'w', function(err, fd) {
    if (err) {
        throw 'could not open file: ' + err;
    }

    // write the contents of the buffer, from position 0 to the end, to the file descriptor returned in opening our file
    fs.write(fd, buffer, 0, buffer.length, null, function(err) {
        if (err) throw 'error writing file: ' + err;
        fs.close(fd, function() {
            console.log('wrote the file successfully');
        });
    });
});

                                    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)


}