A little utility to extend underscore with a couple of methods I wanted, `isCollection` and `complement`, as well as `isNot*` functions to match the `is*` functions.

undermore.js

module.exports = (function () {

  var _ = require('underscore');   

  var isCollection = function(item) {
    return (_.isObject(item) || _.isArray(item) || _.isArguments(item));
  };

  var complement = function(fn) {
    return function() {
      return !fn.apply(null, _.toArray(arguments));
    }
  };
  
  _.mixin({
    isCollection: isCollection,
    complement: complement
  });

  var isaFunctions = _.pick(_, _.chain(_)
                          .functions()
                          .filter(function(fn){return fn.match(/^is[A-Z]/)})
                          .value());

  var opposites = _.reduce(isaFunctions, function(memo, f, fname) {
                                      var name = fname.replace(/^is/,"isNot");
                                      var func = complement(f);
                                      memo[name] = func;
                                      return memo;
  }, {});

  _.mixin(opposites);

  return _;

}).call(this);