Notable ES6 features include having classes moved out of staging, with the class keyword now usable in strict mod without flags, io.js representative Mikeal Rogers said in an email: "[Version] 2.0 has a new version of V8 [version 126.96.36.199]. This means that we've taken on additional ES6 language features and we have a small ABI change -- hence the need for a major version bump. In the future we expect to see more major version upgrades like this as we continue to keep up with V8." The engine has served as an underpinning of Node.js.
Also with io.js 2.0, object literal enhancements have been moved out of staging, with shorthand method and property syntax now usable, he said. Computed property names, meanwhile, are implemented in staging behind the ---harmony-rest-paramaters flag. Unicode escapes are implanted in staging behind the harmony-unicode flag.
Io.js, which forked off Node.js late last year, is billed as an Npm-compatible platform originally based on Node.js. While there has been talk of a reconciliation between the io.js and Node.js camps, which have much overlap in participants, there also has been discussion of io.js serving as a testing ground for Node.js features.