JavaScript How do you properly check if filename exist and generate a suffix before writing it to the directory?

I have a function that writes a file to a directory:

response.pipe(fs.createWriteStream(fullPath))

But before that I want to check if the path already exist, and if so, add a suffix, e.g. file_1.txt (and if that exist, create file_2.txt instead...etc):

// Check if the path already exist
let fullPath = "C:/test/file.txt"
let dir = "C:/test/"
let fileName = "file" 
let fileExt = ".txt"

if (fs.existsSync(fullPath)) {
  // I tried using a while loop but I end up making it too complicated
  ...
}


// Write file to disk
response.pipe(fs.createWriteStream(destinationPath))

Question

How do I properly / efficiently do that?

Answer:1

The while loop is the correct way.

// Check if the path already exist
let fullPath = "C:/test/file.txt"
let dir = "C:/test/"
let fileName = "file" 
let fileExt = ".txt"
let num = 0;

while (fs.existsSync(fullPath)) {
  fullPath = `${dir}${fileName}_${num++}${fileExt}`;
}

After this, fullPath contains the first nonexistent file.

Note that there's a potential race condition. Some other process could create the file after your loop finishes.

Answer:2

If all of your file names are named the same thing + "_#".txt, I think the most (one of the most) efficient ways to check that would be something along the lines of:

Get all files from the directory

var files = [];
fs.readdir(dir, (err, files) => {
  files.forEach(file => {
    files.push(file);
  });
})

You would then sort the array (could be expensive if a lot of files)... then last record would be the highest number which you can easily extract.

Another thing you could do is find the file which has the latest creation date using similar approach using the Stats class from FS.

Answer:3

Returning unique values from multiple data attributes

I have the following markup: <li data-group="bottoms">Pants</li> <li data-group="bottoms">Pants</li> <li data-group="bottoms">Pants</li> <li data-group="tops"&...

returning unique values from a list in excel
sql return unique values

My Android app gets 'Javascript not enabled' message back from POST

I am writing an Android app that requires access to a MySql server. Following examples I have found, I have a php page that sits on the server and does the MySql stuff, and I try to access that from ...

android gets hot
android gets hot while charging
android gets slower over time
android gets hot and battery drains
android gets citizenship
android gets ads
android gets stuck on boot screen
android gets hacked
android gets virus
android gets fido2 certification
android gets slow sometimes
android gets black screen
android get iphone apps
android gets focus
android gets stuck on startup
android gets screen width
android gets lag
android phone gets hot
android auto gets disconnected
android 18 gets absorbed by cell

Programmatically modifying maps based on inner condition

I have a map like this for example const Map = new Map().set('123', [ [ 'foo', 'bar' ] ]).set('456', [ [ 'baz', 'qux' ], [ 'quux', 'corge' ] ]); /* The structure of the Map looks like this: Map {...

UI lag between my javascript and my ported elm

I have a navbar which needs to change colour on scroll. This functionality was originally built with js, however now it has a 'Login' button which is built in elm to perform other functionality. I ...