NODE.js is an open source and cross platform runtime environment for executing JavaScript code outside of a browser
Often used to build backend services (APIs - Aplication Programming Interfaces)
Is ideal for building highly-scalable, data-intensive and real-time backend services. Good points:
- Great for prototyping and agile development
- Superfast and highly scalable
- Is JavaScript like in front end (don't have to learn a new programming language)
- Cleaner and more consistent codebase
- Large ecosystem of open-source libs
Real example: Paypal migrated an app from Java and was built twice as fast with fewer people, with 33% fewer lines of code, 40% fewer files and 2x request/sec with a 35% faster response time
Browsers have their own JS Engine to execute JavaScript code: Chakra (Microsoft Edge), SpiderMonkey (Firefox), v8 (Chrome)... Different engines means that sometimes JavaScript code can behave differently in one browser or another.
In 2009, Ryan Dahl (creator of Node) got the idea to execute JS outside of a browser. He tooks Google's v8 engine (the fastest engine) and embedded it inside a C++ program and called it Node.
Node is a program that includes a v8 JavaScript engine plus additional modules that give capabilities not available inside browsers (file system, network...). Both use the same engine, with different runtime environment.
Node has a non-blocking (asynchronous) architecture. A single thread handle all requests in an event queue.
- Is ideal for I/O intensive apps or network access (we can serve more clients without need to throw in more hardware) and is highly scalable
- Node should not be used for CPU-intensive apps (video encoding, image manipulation services...). As a single thread app, when performing the calculations to serve one client, other clients have to wait.

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