Question: > 
> **Possible Duplicate:**  
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> [Could node.js replace Ruby on Rails completely in the future?](https://stackoverflow.com/questions/3436335/could-node-js-replace-ruby-on-rails-completely-in-the-future) 
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I'm doing bad in understanding the sense of node.js. I understand what it does regarding IO etc., but is it for example a Ruby on Rails replacement? Can I do the same database operations etc.? What about authentication? 

what kind of web or other applications get build on basis of node.js?

Answer: 
> 
> is it for example a ruby on rails replacement?
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IMHO RoR has much longer history/experience/functionality for website development. Node.js itself is a lightweight (low level) framework from which you can take off to build various types of server-side applications (not just web oriented). One of its main advantages is in wide spectrum of [modules](https://github.com/joyent/node/wiki/modules) provided by community of open source developers.

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> Can i do the same database operations etc.?
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Yes, just find the right module for your type of database.

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> What about authentication?
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Modules like [connect](http://senchalabs.github.com/connect/) offers built-in authentication functionality.
Node.JS is to Javascript as EventMachine is to Ruby (and Twisted to Python). It's something completely different from Rails.

To illustrate: the Thin webserver that is often used to serve Rails application was built using EventMachine. So you would need a complete web framework on top of Node.JS to make it a Rails replacement.