ES6-generators-example

You can setup a flexible system using ES6 generators for Node even today

Background

EcmaScript6 (called Harmony) has an excellent feature - generators. They offer a very intuitive way of dealing with asynchronous code (usually in conjunction with promise library like Q). Once I wrapped my mind around using them, I wanted to simplify my projects (typically using promises) using generators.

After looking around, I found that generators are supported pretty much by every tool I use. The only thing stopping me is a requirement to share my module with others, who are still running stable Nodejs 0.10.x without generator support.

Solution

I write all my code as usual, but using EcmaScript6 in folder es6. I run the code using node v0.11 with --harmony command line option, by using an alias harm=node --harmony. I am also using grunt-regenerator to convert every file from ES6 to EcmaScript5 (using regenerator).

// Gruntfile.js
regenerator: {
    all: {
        files: [{
            expand: true,
            cwd: 'es6/',
            src: ['**/*.js'],
            dest: 'es5/'
        }]
    }
}

The generated EcmaScript5 code is committed to the repo too.

runtime

I point at a simple pick-ecmascript.js file from package.json that select which code to run: ES6 or ES5. The script looks at the node version and command line arguments to figure out which version to start. If ES5 is selected, the script also loads a small supporting function by needed to run the converted code (provided by the regenerator)

function isHarmony() {
  if (process.versions.node.split('.')[1] < 11) {
    return false;
  }
  return process.execArgv.some(function (arg) {
    return arg == '--harmony';
  });
}

if (isHarmony()) {
  console.log('Harmony!');
  require('./es6');
} else {
  console.log('ES5 :(');
  require('./node_modules/grunt-regenerator/node_modules/regenerator/runtime/dev.js');
  require('./es5');
}

execution

A typical run using node v0.11 using npm start command

$ npm start

> [email protected] start /Users/gbahmutov/git/es6-generators-example
> node --harmony pick-ecmascript.js

Harmony!
1
2
4
9

Small print

Author: Gleb Bahmutov © 2013

• @bahmutov
• glebbahmutov.com
• blog

License: MIT - do anything with the code, but don't blame me if it does not work.

Support: if you find any problems with this module, email / tweet / open issue on Github