Why NodeJS has 4.x, 5.x, 6.x and 0.1x.x versions, etc.

There are two things to note in response to your question.

• why the jump from 0.x.x to 4.x.x
• Why 4, 5, and 6 versions are almost simultaneous

The Node.js when it was released brought together many of the game's top performers. Like many new / experimental technologies there were many possible paths and people with different ideas. The community could not understand itself and two models of "governance" were desired:

  

"open governance model" as opposed to corporate stewardship

In other words, a more formal group with strict rules and another with more cooperative and more flexible spirit. This led to a breakup and the io.js community was born.

The new, more flexible community has developed faster and released its own versions of Node.js (io.js).

After some time both communities matured and looked back at each other and identified gains in unification. And so it happened, in 2015 the well-active fork community io.js has rejoined the Node.js community, aware of the advantages of re-union.

This gave rise to some versioning challenges and it was decided that the io.js versions would have their own numbers, then the versions stayed like this :

  

io.js : versions 0.1.x to 0.12.x 1.xx to 3.xx Unified Node: versions 4.xx >

How does Node versioning work?

Node versions are LTS * interleaved, ie the even versions are stable and the odd versions are unstable, experimental, and development.

The 0.4 and 0.10 versions were the most used maybe, and stable. Nowadays it is possible to download the versions 4.x.x and 6.x.x . The 5.x.x version is not available on the main page to avoid deceiving those who do not know this. The 4.x.x version received initial support for 30 months, while the 5.x.x version received support only for 8 months or so until the release of the stable version 6.0.0

Notes:

  

LTS - long term support