Strike a Harmony with Node.js and Harmonica

With every new version of Node.js, the platform quietly provides access to experimental features that ship with v8 which may not be quite ready for production use. That doesn’t mean we can’t use those features today, though. And there’s a nearly effortless way to access them.

For those that may be new to Node.js or those who haven’t yet delved into the inner workings of Node.js - the platform runs atop Google’s JavaScript engine, V8 by default. V8 is constantly improving and typically ships with features which may not be stable or ready for production environments, that require command-line flags to enable. Those flags are the harmony flags.

Prior to Node.js v7.6, the asyc/await feature - the feature I’d been most looking forward to - was locked behind the--harmony-async-await flag. There’s a good likelihood that ES6 Modules will arrive in much the same way.

Harmony Flags

Determining what harmony flags are supported by a version of Node.js is easy:

node --v8-options | grep "in progress"

For example, I’m currently on Node.js version 7.8. Running that command, the list of harmony flags shows as follows:

→ node --v8-options | grep "in progress"
  --harmony_array_prototype_values (enable "harmony Array.prototype.values" (in progress))
  --harmony_function_sent (enable "harmony function.sent" (in progress))
  --harmony_sharedarraybuffer (enable "harmony sharedarraybuffer" (in progress))
  --harmony_simd (enable "harmony simd" (in progress))
  --harmony_do_expressions (enable "harmony do-expressions" (in progress))
  --harmony_restrictive_generators (enable "harmony restrictions on generator declarations" (in progress))
  --harmony_regexp_named_captures (enable "harmony regexp named captures" (in progress))
  --harmony_regexp_property (enable "harmony unicode regexp property classes" (in progress))
  --harmony_for_in (enable "harmony for-in syntax" (in progress))
  --harmony_trailing_commas (enable "harmony trailing commas in function parameter lists" (in progress))
  --harmony_class_fields (enable "harmony public fields in class literals" (in progress))

To enable a harmony flag, Node.js typically has to be run from the command-line with the flag and the target entry script as such:

node index.js --harmony_array_prototype_values

Or to enable all harmony flags:

node index.js --harmony

And that can just get tedious for tooling, cross-team development, etc.

An Easy Instrument

Harmonica is an NPM Module that allows developers to use --harmony flags programmatically, which means an end to the need for specifying command-line options for experimental harmony features. If you’ve ever wanted to use experimental features within Gulp tasks, or have a need to run an app through wrappers like forever, this module takes the command-line headache out of the equation.

Setting up Harmonica is painless. Within your entry file (index.js, app.js, etc) place a call to harmonica:

require('harmonica')();

That’s the equivalent to node --harmony. Should you need only specific flags, pass an Array of strings representing the flags you want to enable, without the leading hyphens, as the first parameter.

require('harmonica')([
  'harmony_function_sent',
  'harmony_do_expressions'
]);

And from there, let the module handle initializing the harmony flags you wish to use, with no need to specify them within the terminal or command prompt.

Not All Roses and Rainbows

It’s really important to note that harmony features are not production ready. And as folks have pointed out, some of the experimental / unstable features that are hidden behind harmony flags can come with issues that affect security, performance, etc. It’s never advisable to use harmony features in a production environment unless thoroughly vetted.

Now get to dabbling with the latest that Node.js has to offer!

Cheers!