Cucumber.js step definition transforms

my.feature

# features/my.feature
Feature:
  Scenario: cukes
    Given I have 10 cucumbers in my BaG
    Given I don't have 20 cucumbers in my bAg
    Given I have 98775655 cucumbers in my bag

stepdefs.js

// features/step_definitions/stepdefs.js
var transform = require('./support/transform.js');

module.exports = function () {
  this.Transform(/^(\d+)$/, function (matches) { return parseInt(matches[0]); });
  this.Transform(/^(have|don't have)$/, function (matches) { return matches[0] == 'have'; });
  this.Transform(/^([bB][aA][gG])$/, function () { return 'bag'; });

  this.Given(/^I (have|don't have) (\d+) cucumbers in my (.*)$/, function (has, count, where) {
    console.log('Given...', has, typeof count, where)
  });
}

transform.js

// features/support/transform.js
var transforms = [];

function cast(value) {
  for (var i = 0; i < transforms.length; i++) {
    var transform = transforms[i];
    var matches = transform.pattern.exec(value);
    if (matches) {
      return transform.fn(matches);
    }
  }
  return value;
}

function t(fn) {
  var args = [];
  var body = 'var args = [];';
  for (var i = 0; i < fn.length; i++) {
    args.push('arg' + i);
    body += 'args.push(this.cast(arg' + i + '));\n';
  }
  body += 'return this.fn.apply(this, args);';
  var transformedFn = Function.apply(null, args.concat([body])).bind({fn: fn, cast: cast});
  return transformedFn;
}

module.exports = function () {
  var _defineStep = this.defineStep;
  this.defineStep = function (pattern, fn) {
    _defineStep(pattern, t(fn));
  };
  this.Given = this.When = this.Then = this.defineStep;
  this.Transform = function (pattern, fn) {
    transforms.push({ pattern: pattern, fn: fn });
  };
}