# Lo-Dash v0.5.0-rc.1
A drop-in replacement[*](https://github.com/bestiejs/lodash/wiki/Drop-in-Disclaimer) for Underscore.js, from the devs behind [jsPerf.com](http://jsperf.com), that delivers [performance improvements](http://lodash.com/benchmarks), [bug fixes](https://github.com/bestiejs/lodash#closed-underscorejs-issues), and [additional features](https://github.com/bestiejs/lodash#features).
Lo-Dash’s performance is gained by avoiding slower native methods, instead opting for simplified non-ES5 compliant methods optimized for common usage, and by leveraging function compilation to reduce the number of overall function calls.
## Download
* [Development source](https://raw.github.com/bestiejs/lodash/v0.5.0-rc.1/lodash.js)
* [Production source](https://raw.github.com/bestiejs/lodash/v0.5.0-rc.1/lodash.min.js)
* CDN copies of ≤ [v0.4.2](http://cdnjs.cloudflare.com/ajax/libs/lodash.js/0.4.2/lodash.min.js) are available on [cdnjs](http://cdnjs.com/) thanks to [CloudFlare](http://www.cloudflare.com/)
* For optimal performance, [create a custom build](https://github.com/bestiejs/lodash#custom-builds) with only the features you need
## Dive in
We’ve got [API docs](http://lodash.com/docs), [benchmarks](http://lodash.com/benchmarks), and [unit tests](http://lodash.com/tests).
Create your own benchmarks at [jsPerf](http://jsperf.com), or [search](http://jsperf.com/search?q=lodash) for existing ones.
For a list of upcoming features, check out our [roadmap](https://github.com/bestiejs/lodash/wiki/Roadmap).
## Screencasts
For more information check out these screencasts over Lo-Dash:
* [Introducing Lo-Dash](https://vimeo.com/44154599)
* [Lo-Dash optimizations and custom builds](https://vimeo.com/44154601)
* [Lo-Dash’s origin and why it’s a better utility belt](https://vimeo.com/44154600)
* [Unit testing in Lo-Dash](https://vimeo.com/45865290)
## Features
* AMD loader support ([RequireJS](http://requirejs.org/), [curl.js](https://github.com/cujojs/curl), etc.)
* [_.bind](http://lodash.com/docs#bind) supports *"lazy"* binding
* [_.clone](https://github.com/bestiejs/lodash/tree/master/doc#_clonevalue-deep--guard-thorough) supports *"deep"* cloning
* [_.countBy](https://github.com/bestiejs/lodash/tree/master/doc#_countbycollection-callback--thisarg) as a compainion function for [_.groupBy](http://lodash.com/docs#groupBy) and [_.sortBy](http://lodash.com/docs#sortBy)
* [_.debounce](http://lodash.com/docs#debounce)’ed functions match [_.throttle](http://lodash.com/docs#throttle)’ed functions’ return value behavior
* [_.drop](https://github.com/bestiejs/lodash/tree/master/doc#_dropobject--prop1-prop2-) for the inverse functionality of [_.pick](http://lodash.com/docs#pick)
* [_.forEach](http://lodash.com/docs#forEach) is chainable and supports exiting iteration early
* [_.forIn](http://lodash.com/docs#forIn) for iterating over an object’s own and inherited properties
* [_.forOwn](http://lodash.com/docs#forOwn) for iterating over an object’s own properties
* [_.groupBy](http://lodash.com/docs#groupBy), [_.sortedIndex](http://lodash.com/docs#sortedIndex), and [_.uniq](http://lodash.com/docs#uniq) accept a `thisArg` argument
* [_.indexOf](http://lodash.com/docs#indexOf) and [_.lastIndexOf](http://lodash.com/docs#lastIndexOf) accept a `fromIndex` argument
* [_.merge](https://github.com/bestiejs/lodash/tree/master/doc#_mergeobject--source1-source2--indicator) for a *"deep"* [_.extend](http://lodash.com/docs#extend)
* [_.partial](http://lodash.com/docs#partial) for partial application without `this` binding
* [_.template](http://lodash.com/docs#template) utilizes [sourceURLs](http://www.html5rocks.com/en/tutorials/developertools/sourcemaps/#toc-sourceurl) for easier debugging
* [_.where](https://github.com/bestiejs/lodash/tree/master/doc#_wherecollection-properties) for filtering collections by contained properties
* [_.zipObject](http://lodash.com/docs#zipObject) for composing objects
* [_.contains](http://lodash.com/docs#contains), [_.size](http://lodash.com/docs#size), [_.toArray](http://lodash.com/docs#toArray),
[and more…](http://lodash.com/docs "_.every, _.filter, _.find, _.forEach, _.groupBy, _.invoke, _.map, _.pluck, _.reduce, _.reduceRight, _.reject, _.some, _sortBy") accept strings
## Support
Lo-Dash has been tested in at least Chrome 5-20, Firefox 1.5-13, IE 6-9, Opera 9.25-12.01, Safari 3.0.4-6, Node.js 0.4.8-0.8.2, Narwhal 0.3.2, RingoJS 0.8, and Rhino 1.7RC3.
## Custom builds
Custom builds make it easy to create lightweight versions of Lo-Dash containing only the methods you need.
We handle all the method dependency and alias mapping for you.
* Backbone builds, containing all methods required by Backbone, may be created using the `backbone` modifier argument.
~~~ bash
lodash backbone
~~~
* CSP builds, supporting default Content Security Policy restrictions, may be created using the `csp` modifier argument.
~~~ bash
lodash csp
~~~
* Legacy builds, tailored for older browsers without [ES5 support](http://es5.github.com/), may be created using the `legacy` modifier argument.
~~~ bash
lodash legacy
~~~
* Mobile builds, with IE < 9 bug fixes and method compilation removed, may be created using the `mobile` modifier argument.
~~~ bash
lodash mobile
~~~
* Strict builds, with `_.bindAll`, `_.defaults`, and `_.extend` in [strict mode](http://es5.github.com/#C), may be created using the `strict` modifier argument.
~~~ bash
lodash strict
~~~
* Underscore builds, containing only methods included in Underscore, may be created using the `underscore` modifier argument.
~~~ bash
lodash underscore
~~~
Custom builds may be created in three ways:
1. Use the `category` argument to pass the categories of methods to include in the build.
Valid categories are *"arrays"*, *"chaining"*, *"collections"*, *"functions"*, *"objects"*, and *"utilities"*.
~~~ bash
lodash category=collections,functions
lodash category="collections, functions"
~~~
2. Use the `exclude` argument to pass the names of methods to exclude from the build.
~~~ bash
lodash exclude=union,uniq,zip
lodash exclude="union, uniq, zip"
~~~
3. Use the `include` argument to pass the names of methods to include in the build.
~~~ bash
lodash include=each,filter,map
lodash include="each, filter, map"
~~~
All arguments, except `backbone` with `underscore`, `exclude` with `include`, and `legacy` with `csp`/`mobile`, may be combined.
~~~ bash
lodash backbone legacy category=utilities exclude=first,last
lodash underscore mobile strict category=functions include=pick,uniq
~~~
The `lodash` command-line utility is available when Lo-Dash is installed as a global package (i.e. `npm install -g lodash`).
Custom builds are saved to `lodash.custom.js` and `lodash.custom.min.js`.
## Installation and usage
In browsers:
~~~ html
~~~
Using [npm](http://npmjs.org/):
~~~ bash
npm install lodash
npm install -g lodash
~~~
In [Node.js](http://nodejs.org/) and [RingoJS v0.8.0+](http://ringojs.org/):
~~~ js
var _ = require('lodash');
~~~
In [RingoJS v0.7.0-](http://ringojs.org/):
~~~ js
var _ = require('lodash')._;
~~~
In [Rhino](http://www.mozilla.org/rhino/):
~~~ js
load('lodash.js');
~~~
In an AMD loader like [RequireJS](http://requirejs.org/):
~~~ js
require({
'paths': {
'underscore': 'path/to/lodash'
}
},
['underscore'], function(_) {
console.log(_.VERSION);
});
~~~
## Closed Underscore.js issues (20+)
* Allow iteration of objects with a `length` property [[#148](https://github.com/documentcloud/underscore/issues/148), [#154](https://github.com/documentcloud/underscore/issues/154), [#252](https://github.com/documentcloud/underscore/issues/252), [#448](https://github.com/documentcloud/underscore/issues/448), [#659](https://github.com/documentcloud/underscore/issues/659), [test](https://github.com/bestiejs/lodash/blob/v0.5.0-rc.1/test/test.js#L540-546)]
* Ensure array-like objects with invalid `length` properties are treated like regular objects [[test](https://github.com/bestiejs/lodash/blob/v0.5.0-rc.1/test/test.js#L491-497)]
* Ensure *"Arrays"* methods allow falsey `array` arguments [[test](https://github.com/bestiejs/lodash/blob/v0.5.0-rc.1/test/test.js#L1412-1450)]
* Ensure *"Collections"* methods allow string `collection` arguments [[#247](https://github.com/documentcloud/underscore/issues/247), [#276](https://github.com/documentcloud/underscore/issues/276), [#561](https://github.com/documentcloud/underscore/pull/561), [test](https://github.com/bestiejs/lodash/blob/v0.5.0-rc.1/test/test.js#L499-517)]
* Ensure templates compiled with errors are inspectable [[#666](https://github.com/documentcloud/underscore/issues/666), [test](https://github.com/bestiejs/lodash/blob/v0.5.0-rc.1/test/test.js#L1157-1160)]
* Fix cross-browser object iteration bugs [[#60](https://github.com/documentcloud/underscore/issues/60), [#376](https://github.com/documentcloud/underscore/issues/376), [test](https://github.com/bestiejs/lodash/blob/v0.5.0-rc.1/test/test.js#L551-576)]
* Handle arrays with `undefined` values correctly in IE < 9 [[#601](https://github.com/documentcloud/underscore/issues/601)]
* Methods should work on pages with incorrectly shimmed native methods [[#7](https://github.com/documentcloud/underscore/issues/7), [test](https://github.com/bestiejs/lodash/blob/v0.5.0-rc.1/test/test.js#L117-123)]
* Register as an AMD module, but still export to global [[#431](https://github.com/documentcloud/underscore/pull/431), [test](https://github.com/bestiejs/lodash/blob/v0.5.0-rc.1/test/test.js#L101-115)]
* `_(…)` should return passed wrapper instances [[test](https://github.com/bestiejs/lodash/blob/v0.5.0-rc.1/test/test.js#L135-138)]
* `_.clone` should allow `deep` cloning [[#595](https://github.com/documentcloud/underscore/pull/595), [test](https://github.com/bestiejs/lodash/blob/v0.5.0-rc.1/test/test.js#L197-212)]
* `_.contains` should work with strings [[#667](https://github.com/documentcloud/underscore/pull/667), [test](https://github.com/bestiejs/lodash/blob/v0.5.0-rc.1/test/test.js#L267-276)]
* `_.escape` should return an empty string when passed `null` or `undefined` [[#407](https://github.com/documentcloud/underscore/issues/427), [test](https://github.com/bestiejs/lodash/blob/v0.5.0-rc.1/test/test.js#L367-370)]
* `_.extend` should recursively extend objects [[#379](https://github.com/documentcloud/underscore/pull/379), [test](https://github.com/bestiejs/lodash/blob/v0.5.0-rc.1/test/test.js#L851-873)]
* `_.forEach` should be chainable [[#142](https://github.com/documentcloud/underscore/issues/142), [test](https://github.com/bestiejs/lodash/blob/v0.5.0-rc.1/test/test.js#L486-489)]
* `_.forEach` should exit iteration early [[#211](https://github.com/documentcloud/underscore/issues/211), [test](https://github.com/bestiejs/lodash/blob/v0.5.0-rc.1/test/test.js#L578-597)]
* `_.groupBy` should add values to own, not inherited, properties [[test](https://github.com/bestiejs/lodash/blob/v0.5.0-rc.1/test/test.js#L612-619)]
* `_.isNaN(new Number(NaN))` should return `true` [[test](https://github.com/bestiejs/lodash/blob/v0.5.0-rc.1/test/test.js#L774-776)]
* `_.keys` and `_.size` should work with `arguments` objects cross-browser [[#396](https://github.com/documentcloud/underscore/issues/396), [#653](https://github.com/documentcloud/underscore/issues/653), [test](https://github.com/bestiejs/lodash/blob/v0.5.0-rc.1/test/test.js#L786-788), [test](https://github.com/bestiejs/lodash/blob/v0.5.0-rc.1/test/test.js#L1083-1085)]
* `_.range` should coerce arguments to numbers [[#634](https://github.com/documentcloud/underscore/issues/634), [#683](https://github.com/documentcloud/underscore/issues/683), [test](https://github.com/bestiejs/lodash/blob/v0.5.0-rc.1/test/test.js#L996-999)]
* `_.reduceRight` should pass correct callback arguments when iterating objects [[test](https://github.com/bestiejs/lodash/blob/v0.5.0-rc.1/test/test.js#L1007-1021)]
* `_.size` should return the `length` of string values [[test](https://github.com/bestiejs/lodash/blob/v0.5.0-rc.1/test/test.js#L1066-1068)]
* `_.size` shouldn't error on falsey values [[#650](https://github.com/documentcloud/underscore/pull/650), [test](https://github.com/bestiejs/lodash/blob/v0.5.0-rc.1/test/test.js#L1070-1077)]
* `_.sortedIndex` should support arrays with high `length` values [[test](https://github.com/bestiejs/lodash/blob/v0.5.0-rc.1/test/test.js#L1127-1136)]
* `_.template` should not augment the `options` object [[test](https://github.com/bestiejs/lodash/blob/v0.5.0-rc.1/test/test.js#L1151-1155)]
* `_.throttle` should work when called in a loop [[#502](https://github.com/documentcloud/underscore/issues/502), [test](https://github.com/bestiejs/lodash/blob/v0.5.0-rc.1/test/test.js#L1247-1257)]
* `_.zipObject` should accept less than two arguments [[test](https://github.com/bestiejs/lodash/blob/v0.5.0-rc.1/test/test.js#L1374-1376)]
## Optimized methods (50+)
* `_.bind`
* `_.bindAll`
* `_.clone`
* `_.compact`
* `_.contains`, `_.include`
* `_.defaults`
* `_.defer`
* `_.difference`
* `_.each`
* `_.escape`
* `_.every`, `_.all`
* `_.extend`
* `_.filter`, `_.select`
* `_.find`, `_.detect`
* `_.flatten`
* `_.forEach`, `_.each`
* `_.functions`, `_.methods`
* `_.groupBy`
* `_.indexOf`
* `_.intersection`
* `_.invoke`
* `_.isArguments`
* `_.isDate`
* `_.isEmpty`
* `_.isFinite`
* `_.isFunction`
* `_.isObject`
* `_.isNumber`
* `_.isRegExp`
* `_.isString`
* `_.keys`
* `_.lastIndexOf`
* `_.map`, `_.collect`
* `_.max`
* `_.memoize`
* `_.min`
* `_.mixin`
* `_.pick`
* `_.pluck`
* `_.reduce`, `_.foldl`, `_.inject`
* `_.reject`
* `_.result`
* `_.shuffle`
* `_.some`, `_.any`
* `_.sortBy`
* `_.sortedIndex`
* `_.template`
* `_.throttle`
* `_.times`
* `_.toArray`
* `_.union`
* `_.uniq`, `_.unique`
* `_.values`
* `_.without`
* `_.wrap`
* `_.zip`
* plus all `_(…)` method wrappers
## Release Notes
### v0.5.0-rc.1
* Added `_.countBy`, `_.drop`, `_.merge`, and `_.where`
* Added `csp` *(Content Security Policy)* and `underscore` build options
* Added `deep` cloning support to `_.clone`
* Added support for exiting `_.forEach`, `_.forIn`, and `_.forOwn` early by returning `false` in the `callback`
* Ensured development build works with IE conditional compilation enabled
* Ensured `_.clone` doesn't clone functions, DOM nodes, `arguments` objects, and objects created by constructors other than `Object`
* Ensured `_.filter`’s `callback` can't modify result values
* Ensured `_.isEmpty`, `_.isEquals`, and `_.size` support `arguments` objects
* Ensured `_.isEqual` doesn't inspect DOM nodes, works with objects from other documents, and calls custom `isEqual` methods before checking strict equality
* Ensured `reEvaluateDelimiter` is assigned when `_.templateSettings.evaluate` is undefined
* Made `_.range` coerce arguments to numbers
The full changelog is available [here](https://github.com/bestiejs/lodash/wiki/Changelog).
## BestieJS
Lo-Dash is part of the BestieJS *"Best in Class"* module collection. This means we promote solid browser/environment support, ES5 precedents, unit testing, and plenty of documentation.
## Author
* [John-David Dalton](http://allyoucanleet.com/)
[](https://twitter.com/jdalton "Follow @jdalton on Twitter")
## Contributors
* [Kit Cambridge](http://kitcambridge.github.com/)
[](https://twitter.com/kitcambridge "Follow @kitcambridge on Twitter")
* [Mathias Bynens](http://mathiasbynens.be/)
[](https://twitter.com/mathias "Follow @mathias on Twitter")