Questions about fs.writeFile

I want to use fs.WriteFile in my JS project. I am building an algorithm that outputs random data and I want to give the user the opportunity to save the data as a txt file. I have been able to implement fs.WriteFile in my project, but I have a couple of questions on how to proceed next as the function remains somewhat unclear.

How do I specify that I want to include the contents of various vars? Is it as simple as data = let1 + let2 + let3 and all of the data will be included?
can I add the current date and time in the .txt file name? If so, how?
How do I tell writeFile to save the contents to a .txt file and open a download blob so that people can specify their own download locations?

Thanks in advance!

I've tried looking at basic documentation but its mainly the same: a template using a simple string that saves into the same directory, which is what I don't want.

Solution

For you first question, you are correct. You can just combine different string variables into a larger string variable. See the documentation for string concatenation for more information.

For your second question, yes you can. You can get the current date and time with new Date() and turn it into a variety of formats. For file names, using mydate.toISOString() will probably be the most clean.

Here's an example of both of these in practice:

import fs from 'fs';

// Here's some data that we want to put in the file.
const name = "Bob";
const age = 43;

// Create the data we want to put in our file.
const data = name + '\n' + age;

// Let's grab the date and use it as part of our file name.
const date = new Date();
const fileName = `${date.toISOString()}.txt`;

// Call fs.writeFile to put the data in the file.
fs.writeFile(fileName, data, () => {
  console.log(`Wrote data to ${fileName}.`);
});

Your third question is more complicated and probably worth a separate post. fs.writeFile can't do this for you. You'll have to come up with some mechanism for the user to enter their own file name and build off of that.

Edit:

To address your question in the comments, you might be a little confused with how NodeJS works. NodeJS runs on the server and doesn't have any way to deal with buttons or UIs by default like browser JavaScript does. It might be helpful to look at the differences between the two. So you won't be able to save it to the downloads folder on a button click.

With that said, we can save the file to the user's Downloads folder with the same script I posted above by adding the path to the Downloads folder to the beginning of the file name.

Here's the code above adjusted to do that:

import fs from 'fs';
import os from 'os'; // NEW
import path from 'path'; // NEW

const name = "Bob";
const age = 43;

const data = name + '\n' + age;

const date = new Date();
const fileName = `${date.toISOString()}.txt`;

// Get the user's home directory.
const homedir = os.homedir();

// Append the Downloads directory and fileName to the user's home directory.
const fullPath = path.join(homedir, 'Downloads', fileName);

// Use fullPath here instead of fileName.
fs.writeFile(fullPath, data, () => {
  console.log(`Wrote data to ${fileName}.`);
});