postal.js/example/standard/js/underscore.js

//     Underscore.js 1.1.7
//     (c) 2011 Jeremy Ashkenas, DocumentCloud Inc.
//     Underscore is freely distributable under the MIT license.
//     Portions of Underscore are inspired or borrowed from Prototype,
//     Oliver Steele's Functional, and John Resig's Micro-Templating.
//     For all details and documentation:
//     http://documentcloud.github.com/underscore

(function () {

	// Baseline setup
	// --------------

	// Establish the root object, `window` in the browser, or `global` on the server.
	var root = this;

	// Save the previous value of the `_` variable.
	var previousUnderscore = root._;

	// Establish the object that gets returned to break out of a loop iteration.
	var breaker = {};

	// Save bytes in the minified (but not gzipped) version:
	var ArrayProto = Array.prototype, ObjProto = Object.prototype, FuncProto = Function.prototype;

	// Create quick reference variables for speed access to core prototypes.
	var slice = ArrayProto.slice,
		unshift = ArrayProto.unshift,
		toString = ObjProto.toString,
		hasOwnProperty = ObjProto.hasOwnProperty;

	// All **ECMAScript 5** native function implementations that we hope to use
	// are declared here.
	var
		nativeForEach = ArrayProto.forEach,
		nativeMap = ArrayProto.map,
		nativeReduce = ArrayProto.reduce,
		nativeReduceRight = ArrayProto.reduceRight,
		nativeFilter = ArrayProto.filter,
		nativeEvery = ArrayProto.every,
		nativeSome = ArrayProto.some,
		nativeIndexOf = ArrayProto.indexOf,
		nativeLastIndexOf = ArrayProto.lastIndexOf,
		nativeIsArray = Array.isArray,
		nativeKeys = Object.keys,
		nativeBind = FuncProto.bind;

	// Create a safe reference to the Underscore object for use below.
	var _ = function ( obj ) {
		return new wrapper( obj );
	};

	// Export the Underscore object for **CommonJS**, with backwards-compatibility
	// for the old `require()` API. If we're not in CommonJS, add `_` to the
	// global object.
	if ( typeof module !== 'undefined' && module.exports ) {
		module.exports = _;
		_._ = _;
	} else {
		// Exported as a string, for Closure Compiler "advanced" mode.
		root['_'] = _;
	}

	// Current version.
	_.VERSION = '1.1.7';

	// Collection Functions
	// --------------------

	// The cornerstone, an `each` implementation, aka `forEach`.
	// Handles objects with the built-in `forEach`, arrays, and raw objects.
	// Delegates to **ECMAScript 5**'s native `forEach` if available.
	var each = _.each = _.forEach = function ( obj, iterator, context ) {
		if ( obj == null ) {
			return;
		}
		if ( nativeForEach && obj.forEach === nativeForEach ) {
			obj.forEach( iterator, context );
		} else if ( obj.length === +obj.length ) {
			for ( var i = 0, l = obj.length; i < l; i++ ) {
				if ( i in obj && iterator.call( context, obj[i], i, obj ) === breaker ) {
					return;
				}
			}
		} else {
			for ( var key in obj ) {
				if ( hasOwnProperty.call( obj, key ) ) {
					if ( iterator.call( context, obj[key], key, obj ) === breaker ) {
						return;
					}
				}
			}
		}
	};

	// Return the results of applying the iterator to each element.
	// Delegates to **ECMAScript 5**'s native `map` if available.
	_.map = function ( obj, iterator, context ) {
		var results = [];
		if ( obj == null ) {
			return results;
		}
		if ( nativeMap && obj.map === nativeMap ) {
			return obj.map( iterator, context );
		}
		each( obj, function ( value, index, list ) {
			results[results.length] = iterator.call( context, value, index, list );
		} );
		return results;
	};

	// **Reduce** builds up a single result from a list of values, aka `inject`,
	// or `foldl`. Delegates to **ECMAScript 5**'s native `reduce` if available.
	_.reduce = _.foldl = _.inject = function ( obj, iterator, memo, context ) {
		var initial = memo !== void 0;
		if ( obj == null ) {
			obj = [];
		}
		if ( nativeReduce && obj.reduce === nativeReduce ) {
			if ( context ) {
				iterator = _.bind( iterator, context );
			}
			return initial ? obj.reduce( iterator, memo ) : obj.reduce( iterator );
		}
		each( obj, function ( value, index, list ) {
			if ( !initial ) {
				memo = value;
				initial = true;
			} else {
				memo = iterator.call( context, memo, value, index, list );
			}
		} );
		if ( !initial ) {
			throw new TypeError( "Reduce of empty array with no initial value" );
		}
		return memo;
	};

	// The right-associative version of reduce, also known as `foldr`.
	// Delegates to **ECMAScript 5**'s native `reduceRight` if available.
	_.reduceRight = _.foldr = function ( obj, iterator, memo, context ) {
		if ( obj == null ) {
			obj = [];
		}
		if ( nativeReduceRight && obj.reduceRight === nativeReduceRight ) {
			if ( context ) {
				iterator = _.bind( iterator, context );
			}
			return memo !== void 0 ? obj.reduceRight( iterator, memo ) : obj.reduceRight( iterator );
		}
		var reversed = (_.isArray( obj ) ? obj.slice() : _.toArray( obj )).reverse();
		return _.reduce( reversed, iterator, memo, context );
	};

	// Return the first value which passes a truth test. Aliased as `detect`.
	_.find = _.detect = function ( obj, iterator, context ) {
		var result;
		any( obj, function ( value, index, list ) {
			if ( iterator.call( context, value, index, list ) ) {
				result = value;
				return true;
			}
		} );
		return result;
	};

	// Return all the elements that pass a truth test.
	// Delegates to **ECMAScript 5**'s native `filter` if available.
	// Aliased as `select`.
	_.filter = _.select = function ( obj, iterator, context ) {
		var results = [];
		if ( obj == null ) {
			return results;
		}
		if ( nativeFilter && obj.filter === nativeFilter ) {
			return obj.filter( iterator, context );
		}
		each( obj, function ( value, index, list ) {
			if ( iterator.call( context, value, index, list ) ) {
				results[results.length] = value;
			}
		} );
		return results;
	};

	// Return all the elements for which a truth test fails.
	_.reject = function ( obj, iterator, context ) {
		var results = [];
		if ( obj == null ) {
			return results;
		}
		each( obj, function ( value, index, list ) {
			if ( !iterator.call( context, value, index, list ) ) {
				results[results.length] = value;
			}
		} );
		return results;
	};

	// Determine whether all of the elements match a truth test.
	// Delegates to **ECMAScript 5**'s native `every` if available.
	// Aliased as `all`.
	_.every = _.all = function ( obj, iterator, context ) {
		var result = true;
		if ( obj == null ) {
			return result;
		}
		if ( nativeEvery && obj.every === nativeEvery ) {
			return obj.every( iterator, context );
		}
		each( obj, function ( value, index, list ) {
			if ( !(result = result && iterator.call( context, value, index, list )) ) {
				return breaker;
			}
		} );
		return result;
	};

	// Determine if at least one element in the object matches a truth test.
	// Delegates to **ECMAScript 5**'s native `some` if available.
	// Aliased as `any`.
	var any = _.some = _.any = function ( obj, iterator, context ) {
		iterator = iterator || _.identity;
		var result = false;
		if ( obj == null ) {
			return result;
		}
		if ( nativeSome && obj.some === nativeSome ) {
			return obj.some( iterator, context );
		}
		each( obj, function ( value, index, list ) {
			if ( result |= iterator.call( context, value, index, list ) ) {
				return breaker;
			}
		} );
		return !!result;
	};

	// Determine if a given value is included in the array or object using `===`.
	// Aliased as `contains`.
	_.include = _.contains = function ( obj, target ) {
		var found = false;
		if ( obj == null ) {
			return found;
		}
		if ( nativeIndexOf && obj.indexOf === nativeIndexOf ) {
			return obj.indexOf( target ) != -1;
		}
		any( obj, function ( value ) {
			if ( found = value === target ) {
				return true;
			}
		} );
		return found;
	};

	// Invoke a method (with arguments) on every item in a collection.
	_.invoke = function ( obj, method ) {
		var args = slice.call( arguments, 2 );
		return _.map( obj, function ( value ) {
			return (method.call ? method || value : value[method]).apply( value, args );
		} );
	};

	// Convenience version of a common use case of `map`: fetching a property.
	_.pluck = function ( obj, key ) {
		return _.map( obj, function ( value ) {
			return value[key];
		} );
	};

	// Return the maximum element or (element-based computation).
	_.max = function ( obj, iterator, context ) {
		if ( !iterator && _.isArray( obj ) ) {
			return Math.max.apply( Math, obj );
		}
		var result = {computed : -Infinity};
		each( obj, function ( value, index, list ) {
			var computed = iterator ? iterator.call( context, value, index, list ) : value;
			computed >= result.computed && (result = {value : value, computed : computed});
		} );
		return result.value;
	};

	// Return the minimum element (or element-based computation).
	_.min = function ( obj, iterator, context ) {
		if ( !iterator && _.isArray( obj ) ) {
			return Math.min.apply( Math, obj );
		}
		var result = {computed : Infinity};
		each( obj, function ( value, index, list ) {
			var computed = iterator ? iterator.call( context, value, index, list ) : value;
			computed < result.computed && (result = {value : value, computed : computed});
		} );
		return result.value;
	};

	// Sort the object's values by a criterion produced by an iterator.
	_.sortBy = function ( obj, iterator, context ) {
		return _.pluck( _.map( obj,
			function ( value, index, list ) {
				return {
					value : value,
					criteria : iterator.call( context, value, index, list )
				};
			} ).sort( function ( left, right ) {
				var a = left.criteria, b = right.criteria;
				return a < b ? -1 : a > b ? 1 : 0;
			} ), 'value' );
	};

	// Groups the object's values by a criterion produced by an iterator
	_.groupBy = function ( obj, iterator ) {
		var result = {};
		each( obj, function ( value, index ) {
			var key = iterator( value, index );
			(result[key] || (result[key] = [])).push( value );
		} );
		return result;
	};

	// Use a comparator function to figure out at what index an object should
	// be inserted so as to maintain order. Uses binary search.
	_.sortedIndex = function ( array, obj, iterator ) {
		iterator || (iterator = _.identity);
		var low = 0, high = array.length;
		while ( low < high ) {
			var mid = (low + high) >> 1;
			iterator( array[mid] ) < iterator( obj ) ? low = mid + 1 : high = mid;
		}
		return low;
	};

	// Safely convert anything iterable into a real, live array.
	_.toArray = function ( iterable ) {
		if ( !iterable ) {
			return [];
		}
		if ( iterable.toArray ) {
			return iterable.toArray();
		}
		if ( _.isArray( iterable ) ) {
			return slice.call( iterable );
		}
		if ( _.isArguments( iterable ) ) {
			return slice.call( iterable );
		}
		return _.values( iterable );
	};

	// Return the number of elements in an object.
	_.size = function ( obj ) {
		return _.toArray( obj ).length;
	};

	// Array Functions
	// ---------------

	// Get the first element of an array. Passing **n** will return the first N
	// values in the array. Aliased as `head`. The **guard** check allows it to work
	// with `_.map`.
	_.first = _.head = function ( array, n, guard ) {
		return (n != null) && !guard ? slice.call( array, 0, n ) : array[0];
	};

	// Returns everything but the first entry of the array. Aliased as `tail`.
	// Especially useful on the arguments object. Passing an **index** will return
	// the rest of the values in the array from that index onward. The **guard**
	// check allows it to work with `_.map`.
	_.rest = _.tail = function ( array, index, guard ) {
		return slice.call( array, (index == null) || guard ? 1 : index );
	};

	// Get the last element of an array.
	_.last = function ( array ) {
		return array[array.length - 1];
	};

	// Trim out all falsy values from an array.
	_.compact = function ( array ) {
		return _.filter( array, function ( value ) {
			return !!value;
		} );
	};

	// Return a completely flattened version of an array.
	_.flatten = function ( array ) {
		return _.reduce( array, function ( memo, value ) {
			if ( _.isArray( value ) ) {
				return memo.concat( _.flatten( value ) );
			}
			memo[memo.length] = value;
			return memo;
		}, [] );
	};

	// Return a version of the array that does not contain the specified value(s).
	_.without = function ( array ) {
		return _.difference( array, slice.call( arguments, 1 ) );
	};

	// Produce a duplicate-free version of the array. If the array has already
	// been sorted, you have the option of using a faster algorithm.
	// Aliased as `unique`.
	_.uniq = _.unique = function ( array, isSorted ) {
		return _.reduce( array, function ( memo, el, i ) {
			if ( 0 == i || (isSorted === true ? _.last( memo ) != el : !_.include( memo, el )) ) {
				memo[memo.length] = el;
			}
			return memo;
		}, [] );
	};

	// Produce an array that contains the union: each distinct element from all of
	// the passed-in arrays.
	_.union = function () {
		return _.uniq( _.flatten( arguments ) );
	};

	// Produce an array that contains every item shared between all the
	// passed-in arrays. (Aliased as "intersect" for back-compat.)
	_.intersection = _.intersect = function ( array ) {
		var rest = slice.call( arguments, 1 );
		return _.filter( _.uniq( array ), function ( item ) {
			return _.every( rest, function ( other ) {
				return _.indexOf( other, item ) >= 0;
			} );
		} );
	};

	// Take the difference between one array and another.
	// Only the elements present in just the first array will remain.
	_.difference = function ( array, other ) {
		return _.filter( array, function ( value ) {
			return !_.include( other, value );
		} );
	};

	// Zip together multiple lists into a single array -- elements that share
	// an index go together.
	_.zip = function () {
		var args = slice.call( arguments );
		var length = _.max( _.pluck( args, 'length' ) );
		var results = new Array( length );
		for ( var i = 0; i < length; i++ ) {
			results[i] = _.pluck( args, "" + i );
		}
		return results;
	};

	// If the browser doesn't supply us with indexOf (I'm looking at you, **MSIE**),
	// we need this function. Return the position of the first occurrence of an
	// item in an array, or -1 if the item is not included in the array.
	// Delegates to **ECMAScript 5**'s native `indexOf` if available.
	// If the array is large and already in sort order, pass `true`
	// for **isSorted** to use binary search.
	_.indexOf = function ( array, item, isSorted ) {
		if ( array == null ) {
			return -1;
		}
		var i, l;
		if ( isSorted ) {
			i = _.sortedIndex( array, item );
			return array[i] === item ? i : -1;
		}
		if ( nativeIndexOf && array.indexOf === nativeIndexOf ) {
			return array.indexOf( item );
		}
		for ( i = 0, l = array.length; i < l; i++ ) {
			if ( array[i] === item ) {
				return i;
			}
		}
		return -1;
	};


	// Delegates to **ECMAScript 5**'s native `lastIndexOf` if available.
	_.lastIndexOf = function ( array, item ) {
		if ( array == null ) {
			return -1;
		}
		if ( nativeLastIndexOf && array.lastIndexOf === nativeLastIndexOf ) {
			return array.lastIndexOf( item );
		}
		var i = array.length;
		while ( i-- ) {
			if ( array[i] === item ) {
				return i;
			}
		}
		return -1;
	};

	// Generate an integer Array containing an arithmetic progression. A port of
	// the native Python `range()` function. See
	// [the Python documentation](http://docs.python.org/library/functions.html#range).
	_.range = function ( start, stop, step ) {
		if ( arguments.length <= 1 ) {
			stop = start || 0;
			start = 0;
		}
		step = arguments[2] || 1;

		var len = Math.max( Math.ceil( (stop - start) / step ), 0 );
		var idx = 0;
		var range = new Array( len );

		while ( idx < len ) {
			range[idx++] = start;
			start += step;
		}

		return range;
	};

	// Function (ahem) Functions
	// ------------------

	// Create a function bound to a given object (assigning `this`, and arguments,
	// optionally). Binding with arguments is also known as `curry`.
	// Delegates to **ECMAScript 5**'s native `Function.bind` if available.
	// We check for `func.bind` first, to fail fast when `func` is undefined.
	_.bind = function ( func, obj ) {
		if ( func.bind === nativeBind && nativeBind ) {
			return nativeBind.apply( func, slice.call( arguments, 1 ) );
		}
		var args = slice.call( arguments, 2 );
		return function () {
			return func.apply( obj, args.concat( slice.call( arguments ) ) );
		};
	};

	// Bind all of an object's methods to that object. Useful for ensuring that
	// all callbacks defined on an object belong to it.
	_.bindAll = function ( obj ) {
		var funcs = slice.call( arguments, 1 );
		if ( funcs.length == 0 ) {
			funcs = _.functions( obj );
		}
		each( funcs, function ( f ) {
			obj[f] = _.bind( obj[f], obj );
		} );
		return obj;
	};

	// Memoize an expensive function by storing its results.
	_.memoize = function ( func, hasher ) {
		var memo = {};
		hasher || (hasher = _.identity);
		return function () {
			var key = hasher.apply( this, arguments );
			return hasOwnProperty.call( memo, key ) ? memo[key] : (memo[key] = func.apply( this, arguments ));
		};
	};

	// Delays a function for the given number of milliseconds, and then calls
	// it with the arguments supplied.
	_.delay = function ( func, wait ) {
		var args = slice.call( arguments, 2 );
		return setTimeout( function () {
			return func.apply( func, args );
		}, wait );
	};

	// Defers a function, scheduling it to run after the current call stack has
	// cleared.
	_.defer = function ( func ) {
		return _.delay.apply( _, [func, 1].concat( slice.call( arguments, 1 ) ) );
	};

	// Internal function used to implement `_.throttle` and `_.debounce`.
	var limit = function ( func, wait, debounce ) {
		var timeout;
		return function () {
			var context = this, args = arguments;
			var throttler = function () {
				timeout = null;
				func.apply( context, args );
			};
			if ( debounce ) {
				clearTimeout( timeout );
			}
			if ( debounce || !timeout ) {
				timeout = setTimeout( throttler, wait );
			}
		};
	};

	// Returns a function, that, when invoked, will only be triggered at most once
	// during a given window of time.
	_.throttle = function ( func, wait ) {
		return limit( func, wait, false );
	};

	// Returns a function, that, as long as it continues to be invoked, will not
	// be triggered. The function will be called after it stops being called for
	// N milliseconds.
	_.debounce = function ( func, wait ) {
		return limit( func, wait, true );
	};

	// Returns a function that will be executed at most one time, no matter how
	// often you call it. Useful for lazy initialization.
	_.once = function ( func ) {
		var ran = false, memo;
		return function () {
			if ( ran ) {
				return memo;
			}
			ran = true;
			return memo = func.apply( this, arguments );
		};
	};

	// Returns the first function passed as an argument to the second,
	// allowing you to adjust arguments, run code before and after, and
	// conditionally execute the original function.
	_.wrap = function ( func, wrapper ) {
		return function () {
			var args = [func].concat( slice.call( arguments ) );
			return wrapper.apply( this, args );
		};
	};

	// Returns a function that is the composition of a list of functions, each
	// consuming the return value of the function that follows.
	_.compose = function () {
		var funcs = slice.call( arguments );
		return function () {
			var args = slice.call( arguments );
			for ( var i = funcs.length - 1; i >= 0; i-- ) {
				args = [funcs[i].apply( this, args )];
			}
			return args[0];
		};
	};

	// Returns a function that will only be executed after being called N times.
	_.after = function ( times, func ) {
		return function () {
			if ( --times < 1 ) {
				return func.apply( this, arguments );
			}
		};
	};


	// Object Functions
	// ----------------

	// Retrieve the names of an object's properties.
	// Delegates to **ECMAScript 5**'s native `Object.keys`
	_.keys = nativeKeys || function ( obj ) {
		if ( obj !== Object( obj ) ) {
			throw new TypeError( 'Invalid object' );
		}
		var keys = [];
		for ( var key in obj ) {
			if ( hasOwnProperty.call( obj, key ) ) {
				keys[keys.length] = key;
			}
		}
		return keys;
	};

	// Retrieve the values of an object's properties.
	_.values = function ( obj ) {
		return _.map( obj, _.identity );
	};

	// Return a sorted list of the function names available on the object.
	// Aliased as `methods`
	_.functions = _.methods = function ( obj ) {
		var names = [];
		for ( var key in obj ) {
			if ( _.isFunction( obj[key] ) ) {
				names.push( key );
			}
		}
		return names.sort();
	};

	// Extend a given object with all the properties in passed-in object(s).
	_.extend = function ( obj ) {
		each( slice.call( arguments, 1 ), function ( source ) {
			for ( var prop in source ) {
				if ( source[prop] !== void 0 ) {
					obj[prop] = source[prop];
				}
			}
		} );
		return obj;
	};

	// Fill in a given object with default properties.
	_.defaults = function ( obj ) {
		each( slice.call( arguments, 1 ), function ( source ) {
			for ( var prop in source ) {
				if ( obj[prop] == null ) {
					obj[prop] = source[prop];
				}
			}
		} );
		return obj;
	};

	// Create a (shallow-cloned) duplicate of an object.
	_.clone = function ( obj ) {
		return _.isArray( obj ) ? obj.slice() : _.extend( {}, obj );
	};

	// Invokes interceptor with the obj, and then returns obj.
	// The primary purpose of this method is to "tap into" a method chain, in
	// order to perform operations on intermediate results within the chain.
	_.tap = function ( obj, interceptor ) {
		interceptor( obj );
		return obj;
	};

	// Perform a deep comparison to check if two objects are equal.
	_.isEqual = function ( a, b ) {
		// Check object identity.
		if ( a === b ) {
			return true;
		}
		// Different types?
		var atype = typeof(a), btype = typeof(b);
		if ( atype != btype ) {
			return false;
		}
		// Basic equality test (watch out for coercions).
		if ( a == b ) {
			return true;
		}
		// One is falsy and the other truthy.
		if ( (!a && b) || (a && !b) ) {
			return false;
		}
		// Unwrap any wrapped objects.
		if ( a._chain ) {
			a = a._wrapped;
		}
		if ( b._chain ) {
			b = b._wrapped;
		}
		// One of them implements an isEqual()?
		if ( a.isEqual ) {
			return a.isEqual( b );
		}
		if ( b.isEqual ) {
			return b.isEqual( a );
		}
		// Check dates' integer values.
		if ( _.isDate( a ) && _.isDate( b ) ) {
			return a.getTime() === b.getTime();
		}
		// Both are NaN?
		if ( _.isNaN( a ) && _.isNaN( b ) ) {
			return false;
		}
		// Compare regular expressions.
		if ( _.isRegExp( a ) && _.isRegExp( b ) ) {
			return a.source === b.source &&
			       a.global === b.global &&
			       a.ignoreCase === b.ignoreCase &&
			       a.multiline === b.multiline;
		}
		// If a is not an object by this point, we can't handle it.
		if ( atype !== 'object' ) {
			return false;
		}
		// Check for different array lengths before comparing contents.
		if ( a.length && (a.length !== b.length) ) {
			return false;
		}
		// Nothing else worked, deep compare the contents.
		var aKeys = _.keys( a ), bKeys = _.keys( b );
		// Different object sizes?
		if ( aKeys.length != bKeys.length ) {
			return false;
		}
		// Recursive comparison of contents.
		for ( var key in a ) {
			if ( !(key in b) || !_.isEqual( a[key], b[key] ) ) {
				return false;
			}
		}
		return true;
	};

	// Is a given array or object empty?
	_.isEmpty = function ( obj ) {
		if ( _.isArray( obj ) || _.isString( obj ) ) {
			return obj.length === 0;
		}
		for ( var key in obj ) {
			if ( hasOwnProperty.call( obj, key ) ) {
				return false;
			}
		}
		return true;
	};

	// Is a given value a DOM element?
	_.isElement = function ( obj ) {
		return !!(obj && obj.nodeType == 1);
	};

	// Is a given value an array?
	// Delegates to ECMA5's native Array.isArray
	_.isArray = nativeIsArray || function ( obj ) {
		return toString.call( obj ) === '[object Array]';
	};

	// Is a given variable an object?
	_.isObject = function ( obj ) {
		return obj === Object( obj );
	};

	// Is a given variable an arguments object?
	_.isArguments = function ( obj ) {
		return !!(obj && hasOwnProperty.call( obj, 'callee' ));
	};

	// Is a given value a function?
	_.isFunction = function ( obj ) {
		return !!(obj && obj.constructor && obj.call && obj.apply);
	};

	// Is a given value a string?
	_.isString = function ( obj ) {
		return !!(obj === '' || (obj && obj.charCodeAt && obj.substr));
	};

	// Is a given value a number?
	_.isNumber = function ( obj ) {
		return !!(obj === 0 || (obj && obj.toExponential && obj.toFixed));
	};

	// Is the given value `NaN`? `NaN` happens to be the only value in JavaScript
	// that does not equal itself.
	_.isNaN = function ( obj ) {
		return obj !== obj;
	};

	// Is a given value a boolean?
	_.isBoolean = function ( obj ) {
		return obj === true || obj === false;
	};

	// Is a given value a date?
	_.isDate = function ( obj ) {
		return !!(obj && obj.getTimezoneOffset && obj.setUTCFullYear);
	};

	// Is the given value a regular expression?
	_.isRegExp = function ( obj ) {
		return !!(obj && obj.test && obj.exec && (obj.ignoreCase || obj.ignoreCase === false));
	};

	// Is a given value equal to null?
	_.isNull = function ( obj ) {
		return obj === null;
	};

	// Is a given variable undefined?
	_.isUndefined = function ( obj ) {
		return obj === void 0;
	};

	// Utility Functions
	// -----------------

	// Run Underscore.js in *noConflict* mode, returning the `_` variable to its
	// previous owner. Returns a reference to the Underscore object.
	_.noConflict = function () {
		root._ = previousUnderscore;
		return this;
	};

	// Keep the identity function around for default iterators.
	_.identity = function ( value ) {
		return value;
	};

	// Run a function **n** times.
	_.times = function ( n, iterator, context ) {
		for ( var i = 0; i < n; i++ ) {
			iterator.call( context, i );
		}
	};

	// Add your own custom functions to the Underscore object, ensuring that
	// they're correctly added to the OOP wrapper as well.
	_.mixin = function ( obj ) {
		each( _.functions( obj ), function ( name ) {
			addToWrapper( name, _[name] = obj[name] );
		} );
	};

	// Generate a unique integer id (unique within the entire client session).
	// Useful for temporary DOM ids.
	var idCounter = 0;
	_.uniqueId = function ( prefix ) {
		var id = idCounter++;
		return prefix ? prefix + id : id;
	};

	// By default, Underscore uses ERB-style template delimiters, change the
	// following template settings to use alternative delimiters.
	_.templateSettings = {
		evaluate : /<%([\s\S]+?)%>/g,
		interpolate : /<%=([\s\S]+?)%>/g
	};

	// JavaScript micro-templating, similar to John Resig's implementation.
	// Underscore templating handles arbitrary delimiters, preserves whitespace,
	// and correctly escapes quotes within interpolated code.
	_.template = function ( str, data ) {
		var c = _.templateSettings;
		var tmpl = 'var __p=[],print=function(){__p.push.apply(__p,arguments);};' +
		           'with(obj||{}){__p.push(\'' +
		           str.replace( /\\/g, '\\\\' )
			           .replace( /'/g, "\\'" )
			           .replace( c.interpolate, function ( match, code ) {
				           return "'," + code.replace( /\\'/g, "'" ) + ",'";
			           } )
			           .replace( c.evaluate || null, function ( match, code ) {
				           return "');" + code.replace( /\\'/g, "'" )
					           .replace( /[\r\n\t]/g, ' ' ) + "__p.push('";
			           } )
			           .replace( /\r/g, '\\r' )
			           .replace( /\n/g, '\\n' )
			           .replace( /\t/g, '\\t' )
			+ "');}return __p.join('');";
		var func = new Function( 'obj', tmpl );
		return data ? func( data ) : func;
	};

	// The OOP Wrapper
	// ---------------

	// If Underscore is called as a function, it returns a wrapped object that
	// can be used OO-style. This wrapper holds altered versions of all the
	// underscore functions. Wrapped objects may be chained.
	var wrapper = function ( obj ) {
		this._wrapped = obj;
	};

	// Expose `wrapper.prototype` as `_.prototype`
	_.prototype = wrapper.prototype;

	// Helper function to continue chaining intermediate results.
	var result = function ( obj, chain ) {
		return chain ? _( obj ).chain() : obj;
	};

	// A method to easily add functions to the OOP wrapper.
	var addToWrapper = function ( name, func ) {
		wrapper.prototype[name] = function () {
			var args = slice.call( arguments );
			unshift.call( args, this._wrapped );
			return result( func.apply( _, args ), this._chain );
		};
	};

	// Add all of the Underscore functions to the wrapper object.
	_.mixin( _ );

	// Add all mutator Array functions to the wrapper.
	each( ['pop', 'push', 'reverse', 'shift', 'sort', 'splice', 'unshift'], function ( name ) {
		var method = ArrayProto[name];
		wrapper.prototype[name] = function () {
			method.apply( this._wrapped, arguments );
			return result( this._wrapped, this._chain );
		};
	} );

	// Add all accessor Array functions to the wrapper.
	each( ['concat', 'join', 'slice'], function ( name ) {
		var method = ArrayProto[name];
		wrapper.prototype[name] = function () {
			return result( method.apply( this._wrapped, arguments ), this._chain );
		};
	} );

	// Start chaining a wrapped Underscore object.
	wrapper.prototype.chain = function () {
		this._chain = true;
		return this;
	};

	// Extracts the result from a wrapped and chained object.
	wrapper.prototype.value = function () {
		return this._wrapped;
	};

})();