Observe file changes with node.js

I have the following UseCase:

A creates a Chat and invites B and C - On the Server A creates a File. A, B and C writes messages into this file. A, B and C read this file.

I want a to create a file on server and observe this file if anybody else writes something into this file send the new content back with websockets.

So, any change of this file should be observed by my node.js application.

How can I observe files-changes? Is this possible with node js without locking the files?

If not possible with files, would it be possible with database object (NoSQL)

Good news is that you can observe filechanges with Node's API.

Reading the Node.js API doc is very useful when figuring these things out. It's an invaluable source. :)

This however doesn't give you access to the contents that has been written into the file. You can maybe use the fs.appendFile(); function so that when something is being written into the file you emit an event to something else that "logs" your new data that is being written.

fs.watch(): Directly pasted from the docs

fs.watch('somedir', function (event, filename) {
    console.log('event is: ' + event);
    if (filename) {
        console.log('filename provided: ' + filename);
    } else {
        console.log('filename not provided');
    }
});

Read here about the fs.watch(); function

EDIT: You can use the function

fs.watchFile();

Read here about the fs.watchFile(); function

This will allow you to watch a file for changes. Ie. whenever it is accessed by some other processes of any kind.

I do not think you need to have observe file changes or use a NoSQL database for this(if you do not want to). My advice would be to look at events(Observer pattern). There are more than enough tutorials on this topic available online(Google). For example Felix's article aboutUsing EventEmitters

This publish/subcribe semantic can also be achieved with NoSQL. In Redis for example I think you should have a look at pubsub.

In MongoDB I think tailable cursors is what you are looking for. On there blog they have a post explaining pub/sub.