This, like the C++ declaration of the same name, declares that the reference name (“firstName”) can never point anywhere else it doesn’t insist that the object to which the reference points cannot change.

One of these conventions is that of immutability, which ECMAScript 2015 embodies through use of a const declaration: const firstName = 'Ted'

Some of the simplest changes to the language simply embrace modes of programming that have been widespread convention in the ecosystem and community for some time now. In this installment, I’ll go over some of the more interesting and important features of ECMAScript 2015, and in a future piece, I’ll look at what using MEAN in the more modern style would be like (essentially, now that you’ve got a firm footing on how MEAN applications operate, I’ll reboot the code base completely more on that then). Fortunately, it’s trivial to do so, because there are good reasons to do so. If your JavaScript code isn’t starting to use it, then it’s high time to start.

What you might not realize is that JavaScript (which is actually officially known as ECMAScript) has a new version of the language, ECMAScript 2015. Volume 31 Number 8 How To Be MEAN: Exploring ECMAScript

Ecmascript 2015