A tiny hacked together version of a few essential Underscore functions. Great for use in small scripts where you don't want to load the entire library.

mini_underscore.js

// Setup the methods
var _ = {

  init: function() {
    var _this = this;
    // Create the comparitor methods e.g. isString
    this.each(['Arguments', 'Function', 'String', 'Number', 'Date', 'RegExp'], function(name) {
      _this['is' + name] = function(obj) {
        return toString.call(obj) == '[object ' + name + ']';
      };
    });
  },

  each: function(obj, iterator, context) {
    if (obj === null) return;
    if (obj.length === +obj.length) {
      for (var i = 0, l = obj.length; i < l; i++) {
        if (iterator.call(context, obj[i], i, obj) === {}) return;
      }
    } else {
      for (var key in obj) {
        if (obj[key]) {
          if (iterator.call(context, obj[key], key, obj) === {}) return;
        }
      }
    }
  },

  // Works on arrays
  contains: function(array, target) {
    var index = array.indexOf(target);
    if (index === -1) {
      return false;
    } else {
      return true;
    }
  },

  isObject: function(obj) {
    return obj === Object(obj);
  },

  isArray: function(obj) {
    return toString.call(obj) == '[object Array]';
  }

};

// Do some things on start (create isString, isFunction etc)
_.init();