Wrapping a callback-based function into an ES6 Generator (requires node 0.11+)

generator_wrapper.js

var q = require('q')

function generatorify(fn, context) {
    return function() {
        var deferred = q.defer(),
            callback = makeCallback(deferred),
            args = Array.prototype.slice.call(arguments).concat(callback);
        fn.apply(context, args);
        return deferred.promise;
    };
}

function makeCallback(deferred) {
    return function (err) {
        if (err) {
            deferred.reject(err);
        } else if (arguments.length < 2) {
            deferred.resolve();
        } else if (arguments.length === 2) {
            deferred.resolve(arguments[1]);
        } else {
            deferred.resolve(Array.prototype.slice.call(arguments, 1));
        }
    };
}
    
// This is monkey patching so don't do it lightly
Function.prototype.generator = function (context) {
  return generatorify(this, context);
};

/// Usage

function callbackBasedFunction(arg, callback) {
  callback(null, arg + 1);
}

function *generator() {
  var genFunction = generatorify(callbackBasedFunction);
  result = yield genFunction(2);
  assert result == 3;
  
  // or with monkey patching
  result = yield callbackBasedFunction.generator(null)(2)
}