As mentioned in Chapter 1, Why Node.js?, the release of Node.js v4 in 2015 shows the platform coming to maturity. If you've used Node.js before the end of 2015, you would have seen version numbers such as v0.8.0 or v0.12.0. So why the leap to v4.0.0?
Node.js is an open-source project with a corporate sponsor, Joyent. This means that a single company has a lot of influence over the direction of Node.js, but anyone can create their own fork of the source code. This is exactly what happened at the end of 2014. A group of major contributors to Node.js split the project to create a new fork, named io.js. A few key properties of io.js were:
A more regular release cycle, keeping more up-to-date with the underlying V8 engine, to take advantage of performance improvements and newer JavaScript language features
A move to semantic versioning (see http://semver.org/), resulting in major version numbers increasing more...