Monkey patch bringing Mocha's --grep and --invert to Cucumber.js

grep.js

function unquote(value) {
  return /^'.*'|".*"$/.test(value) ? value.slice(1, -1) : value;
}

module.exports = function (options) {

  process.argv.reduce(function (obj, value) {
    var groups = /^--(\w+)(?::(.+))?$/.exec(value);
    if (groups !== null) {
      obj[groups[1]] = unquote(groups[2] || '');
    }
    return obj;
  }, options || (options = {}));

  var normalize = typeof options.normalize === 'function' ? options.normalize :
    function (value) {
      return value.toLowerCase();
    };

  if (options.grep) {
    var grep = normalize(options.grep);
    var invert = options.invert === '';
    var runtimeModuleId = Object.keys(require.cache).filter(function (moduleId) {
      return moduleId.indexOf('cucumber/lib/cucumber/runtime.js') > 0;
    });
    var Runtime = require.cache[runtimeModuleId[0]].exports;
    var OriginalAstTreeWalker = Runtime.AstTreeWalker;
    Runtime.AstTreeWalker = function () {
      var result = OriginalAstTreeWalker.apply(this, arguments);
      var originalVisitScenario = result.visitScenario;
      result.visitScenario = function (scenario, callback) {
        var match = !!~normalize(scenario.getName()).indexOf(grep);
        if (match ^ invert) {
          originalVisitScenario.apply(this, arguments);
        } else {
          callback();
        }
      };
      return result;
    };
  }

};

Another option would be to override step.acceptVisitor on BeforeScenario event (which is a much better approach really).