functional.js

var Functional = {
  isFunction: function(obj) {
    return toString.call(obj) === "[object Function]";
  },

  reduce: function(accumulator, object, callback) {
    var name, i = 0,
            length = object.length,
            isObj = length === undefined || Functional.isFunction(object);

    var acc = accumulator;

    if (isObj) {
      for (name in object) {
        if(object.hasOwnProperty(name))
          acc = callback.call(object, acc, object[ name ], name);
      }
    } else {
      for (var value = object[0]; i < length; value = object[++i]) {
        acc = callback.call(object, acc, value, i);
      }
    }

    return acc;
  },

  map: function(object, callback) {
    return Functional.reduce([], object, function(acc, value, index_key) {
      var m = callback.call(object, value, index_key);
      acc.push(m);
      return acc;
    });
  },

  each: function(object, callback) {
    return Functional.reduce(null, object, function(acc, value, index_key) {
      callback.call(object, value, index_key);
      return null;
    });
  },

  filter: function(object, callback) {
    var isObj = object.length === undefined || Functional.isFunction(object);
    if (isObj) {
      return Functional.reduce({}, object, function(acc, value, index_key) {
        if(callback.call(object, value, index_key)){
          acc[index_key] = value;
        }
        return acc;
      });
    } else {
      return Functional.reduce([], object, function(acc, value, index_key) {
        if(callback.call(object, value, index_key)){
          acc.push(value);
        }
        return acc;
      });
    }

  }
};