Node’s Niche

Since JavaScript’s first appearance in 1995, it has been solving problems all along the front-end/back-end spectrum. The following figure shows this spectrum and where Node.js fits within it.

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Figure 2. Node’s place in the JavaScript spectrum

In the web browser on the right, much of the scripting involves waiting for user interaction. Click here, drag that, choose a file, etc. JavaScript has been extraordinarily successful in this space.

On the left, back-end databases are investing heavily in JavaScript. Document-oriented databases like MongoDB and CouchDB use JavaScript extensively—from modifying records to ad-hoc queries and mapreduce jobs. Other datastores, like Neo4j and Elasticsearch, present data in JavaScript Object Notation (JSON). These days, you can even write SQL functions for Postgres in JavaScript with the right plug-in.

Many middleware tasks are I/O-bound, just like client-side scripting and databases. These server-side programs often have to wait for things like a database result, feedback from a third-party web service, or incoming connection requests. Node.js is designed for exactly these kinds of applications.