IO.js Overview

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Version 1.0.0 of io.js was released today. This post is going to give you an overview of what io.js is, what the differences and benefits are and what the aim of the project is.

io.js - a node.js fork

The beginning – how it started

First of all, io.js is a fork of Node.js, and was forked by Fedor Indutny. With that said, Fedor is not the leader of the project, io.js is incorporated as an open governance structure. The key people included in the fork are:

But why did this fork happen?

In July, 2014 they started working with Joyent to ensure that the contributors and the community has the ability to help fix the problems that Node.js faces / will face.

Then in August Node Forward was started to help improve Node.js:

A broad community effort to improve Node, JavaScript, and their ecosystem through open collaboration.

Due to trademark restrictions, the guys could not do a release – but luckily for the community, all those efforts are incorporated into io.js.

After this, Fedor decided to fork Node.js under the name io.js.

The main differences

As you could have already noticed, io.js introduces proper semver, starting with 1.0.0. Also, io.js comes with nightly builds too.

But what’s really great about this release is the updated V8 engine (from version in Node.js v0.10.35 and 3.26.33 in Node.js v0.11.14 to for io.js v1.0.0), which brings us ES6 features, without the --harmony flag – at least those that don’t require a flag in V8 neither.

What about the staging/in-progress features?

All the new features that are considered staging/in-progress by the V8 team are available under the flags starting with --harmony. These are not meant for production systems.

Changes in the core modules

io.js not only brings us ES6, but also new (experimental) core modules and new features/fixes to the existing ones as well.

Available ES6 features

The following list of features are available without using any flags:

  • Block scoping (letconst)
  • Collections (MapWeakMapSetWeakSet)
  • Generators
  • Binary and Octal literals
  • Promises
  • New String methods
  • Symbols
  • Template strings

You can always check which version of V8 is used by your installed io.js simply, with:

iojs -p process.versions.v8

With this information you can check the available features. Also, you can check this ES6 compat-table as well.

New modules

io.js ships with new core modules as well, that can be used without installing from NPM. These are:

  • smalloc: a new core module for doing (external) raw memory allocation/deallocation/copying in JavaScript
  • v8: core module for interfacing directly with the V8 engine

For the complete API Reference, check:

For the complete changelog, check:

Get started

To get started with io.js, visit and download the installer for your system.

After installing it, you can simply start your application the very same way you did with Node.js:

iojs app.js

If you are used to nvm, then we have good news for you: an io.js compatible version is coming soon!

I would encourage you to test your modules with io.js, and report to if you find something unexpected.

What’s next?

On the longer run io.js and Node.js will be merged back together – at least that’s the plan. We hope that the project accomplishes its goals, and help the JavaScript community move forward.

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