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), delivering[performance](http://lodash.com/benchmarks),[bug fixes](https://github.com/bestiejs/lodash#resolved-underscorejs-issues-30), 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.

*[Development source](https://raw.github.com/bestiejs/lodash/v0.6.0/lodash.js)

*[Production source](https://raw.github.com/bestiejs/lodash/v0.6.0/lodash.min.js)

*[Development source](https://raw.github.com/bestiejs/lodash/v0.6.1/lodash.js)

*[Production source](https://raw.github.com/bestiejs/lodash/v0.6.1/lodash.min.js)

* CDN copies of ≤[v0.6.0](http://cdnjs.cloudflare.com/ajax/libs/lodash.js/0.6.0/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

* 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/v0.6.0/test/test.js#L578-584)]

* Ensure array-like objects with invalid`length` properties are treated like regular objects[[test](https://github.com/bestiejs/lodash/blob/v0.6.0/test/test.js#L526-536)]

* Ensure*“Arrays”*, “Collections”, and “Objects” methods don’t error when passed falsey arguments[[#650](https://github.com/documentcloud/underscore/pull/650),[test](https://github.com/bestiejs/lodash/blob/v0.6.0/test/test.js#L1668-1703)]

* 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/v0.6.0/test/test.js#L538-555)]

* Ensure templates compiled with errors are inspectable[[#666](https://github.com/documentcloud/underscore/issues/666),[test](https://github.com/bestiejs/lodash/blob/v0.6.0/test/test.js#L1383-1386)]

* 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/v0.6.0/test/test.js#L589-614)]

* 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/v0.6.1/test/test.js#L578-584)]

* Ensure array-like objects with invalid`length` properties are treated like regular objects[[test](https://github.com/bestiejs/lodash/blob/v0.6.1/test/test.js#L526-536)]

* Ensure*“Arrays”*, “Collections”, and “Objects” methods don’t error when passed falsey arguments[[#650](https://github.com/documentcloud/underscore/pull/650),[test](https://github.com/bestiejs/lodash/blob/v0.6.1/test/test.js#L1668-1703)]

* 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/v0.6.1/test/test.js#L538-555)]

* Ensure templates compiled with errors are inspectable[[#666](https://github.com/documentcloud/underscore/issues/666),[test](https://github.com/bestiejs/lodash/blob/v0.6.1/test/test.js#L1383-1386)]

* 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/v0.6.1/test/test.js#L589-614)]

* 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/v0.6.0/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/v0.6.0/test/test.js#L101-115)]

*`_(…)` should return passed wrapper instances[[test](https://github.com/bestiejs/lodash/blob/v0.6.0/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/v0.6.0/test/test.js#L205-220)]

*`_.contains` should work with strings[[#667](https://github.com/documentcloud/underscore/pull/667),[test](https://github.com/bestiejs/lodash/blob/v0.6.0/test/test.js#L275-284)]

*`_.countBy` and`_.groupBy` should only add values to own, not inherited, properties[[test](https://github.com/bestiejs/lodash/blob/v0.6.0/test/test.js#L292-299)]

*`_.escape` should return an empty string when passed`null` or`undefined`[[#427](https://github.com/documentcloud/underscore/issues/427),[test](https://github.com/bestiejs/lodash/blob/v0.6.0/test/test.js#L402-405)]

*`_.extend` should recursively extend objects[[#379](https://github.com/documentcloud/underscore/pull/379),[#718](https://github.com/documentcloud/underscore/issues/718),[test](https://github.com/bestiejs/lodash/blob/v0.6.0/test/test.js#L979-1001)]

*`_.forEach` should be chainable[[#142](https://github.com/documentcloud/underscore/issues/142),[test](https://github.com/bestiejs/lodash/blob/v0.6.0/test/test.js#L521-524)]

*`_.forEach` should allow exiting iteration early[[#211](https://github.com/documentcloud/underscore/issues/211),[test](https://github.com/bestiejs/lodash/blob/v0.6.0/test/test.js#L616-635)]

*`_.isElement` should use strict equality for its duck type check[[test](https://github.com/bestiejs/lodash/blob/v0.6.0/test/test.js#L731-740)]

*`_.isEmpty` and`_.size` should support jQuery/MooTools DOM query collections[[#690](https://github.com/documentcloud/underscore/pull/690),[test](https://github.com/bestiejs/lodash/blob/v0.6.0/test/test.js#L767-772)]

*`_.isEqual` should return`true` for like-objects from different documents[[test](https://github.com/bestiejs/lodash/blob/v0.6.0/test/test.js#L808-828)]

*`_.isObject` should avoid V8 bug[#2291](http://code.google.com/p/v8/issues/detail?id=2291)[[#605](https://github.com/documentcloud/underscore/issues/605),[test](https://github.com/bestiejs/lodash/blob/v0.6.0/test/test.js#L836-848)]

*`_.isNaN(new Number(NaN))` should return`true`[[test](https://github.com/bestiejs/lodash/blob/v0.6.0/test/test.js#L856-858)]

*`_.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/v0.6.0/test/test.js#L912-914)]

* 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/v0.6.1/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/v0.6.1/test/test.js#L101-115)]

*`_(…)` should return passed wrapper instances[[test](https://github.com/bestiejs/lodash/blob/v0.6.1/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/v0.6.1/test/test.js#L205-220)]

*`_.contains` should work with strings[[#667](https://github.com/documentcloud/underscore/pull/667),[test](https://github.com/bestiejs/lodash/blob/v0.6.1/test/test.js#L275-284)]

*`_.countBy` and`_.groupBy` should only add values to own, not inherited, properties[[test](https://github.com/bestiejs/lodash/blob/v0.6.1/test/test.js#L292-299)]

*`_.escape` should return an empty string when passed`null` or`undefined`[[#427](https://github.com/documentcloud/underscore/issues/427),[test](https://github.com/bestiejs/lodash/blob/v0.6.1/test/test.js#L402-405)]

*`_.extend` should recursively extend objects[[#379](https://github.com/documentcloud/underscore/pull/379),[#718](https://github.com/documentcloud/underscore/issues/718),[test](https://github.com/bestiejs/lodash/blob/v0.6.1/test/test.js#L979-1001)]

*`_.forEach` should be chainable[[#142](https://github.com/documentcloud/underscore/issues/142),[test](https://github.com/bestiejs/lodash/blob/v0.6.1/test/test.js#L521-524)]

*`_.forEach` should allow exiting iteration early[[#211](https://github.com/documentcloud/underscore/issues/211),[test](https://github.com/bestiejs/lodash/blob/v0.6.1/test/test.js#L616-635)]

*`_.isElement` should use strict equality for its duck type check[[test](https://github.com/bestiejs/lodash/blob/v0.6.1/test/test.js#L731-740)]

*`_.isEmpty` and`_.size` should support jQuery/MooTools DOM query collections[[#690](https://github.com/documentcloud/underscore/pull/690),[test](https://github.com/bestiejs/lodash/blob/v0.6.1/test/test.js#L767-772)]

*`_.isEqual` should return`true` for like-objects from different documents[[test](https://github.com/bestiejs/lodash/blob/v0.6.1/test/test.js#L808-828)]

*`_.isObject` should avoid V8 bug[#2291](http://code.google.com/p/v8/issues/detail?id=2291)[[#605](https://github.com/documentcloud/underscore/issues/605),[test](https://github.com/bestiejs/lodash/blob/v0.6.1/test/test.js#L836-848)]

*`_.isNaN(new Number(NaN))` should return`true`[[test](https://github.com/bestiejs/lodash/blob/v0.6.1/test/test.js#L856-858)]

*`_.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/v0.6.1/test/test.js#L912-914)]

*`_.once` should free the given function for garbage collection[[#693](https://github.com/documentcloud/underscore/pull/693)]

*`_.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/v0.6.0/test/test.js#L1170-1173)]

*`_.reduceRight` should pass correct callback arguments when iterating objects[[test](https://github.com/bestiejs/lodash/blob/v0.6.0/test/test.js#L1205-1219)]

*`_.size` should return the`length` of string values[[test](https://github.com/bestiejs/lodash/blob/v0.6.0/test/test.js#L1263-1265)]

*`_.sortedIndex` should support arrays with high`length` values[[test](https://github.com/bestiejs/lodash/blob/v0.6.0/test/test.js#L1353-1362)]

*`_.template` should not augment the`options` object[[test](https://github.com/bestiejs/lodash/blob/v0.6.0/test/test.js#L1377-1381)]

*`_.throttle` should work when called in a loop[[#502](https://github.com/documentcloud/underscore/issues/502),[test](https://github.com/bestiejs/lodash/blob/v0.6.0/test/test.js#L1473-1483)]

*`_.toArray` uses custom`toArray` methods of arrays and strings[[test](https://github.com/bestiejs/lodash/blob/v0.6.0/test/test.js#L1510-1518)]

*`_.zipObject` should accept less than two arguments[[test](https://github.com/bestiejs/lodash/blob/v0.6.0/test/test.js#L1630-1632)]

*`_.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/v0.6.1/test/test.js#L1170-1173)]

*`_.reduceRight` should pass correct callback arguments when iterating objects[[test](https://github.com/bestiejs/lodash/blob/v0.6.1/test/test.js#L1205-1219)]

*`_.size` should return the`length` of string values[[test](https://github.com/bestiejs/lodash/blob/v0.6.1/test/test.js#L1263-1265)]

*`_.sortedIndex` should support arrays with high`length` values[[test](https://github.com/bestiejs/lodash/blob/v0.6.1/test/test.js#L1353-1362)]

*`_.template` should not augment the`options` object[[test](https://github.com/bestiejs/lodash/blob/v0.6.1/test/test.js#L1377-1381)]

*`_.throttle` should work when called in a loop[[#502](https://github.com/documentcloud/underscore/issues/502),[test](https://github.com/bestiejs/lodash/blob/v0.6.1/test/test.js#L1473-1483)]

*`_.toArray` uses custom`toArray` methods of arrays and strings[[test](https://github.com/bestiejs/lodash/blob/v0.6.1/test/test.js#L1510-1518)]

*`_.zipObject` should accept less than two arguments[[test](https://github.com/bestiejs/lodash/blob/v0.6.1/test/test.js#L1630-1632)]

* Ensured IE conditional compilation isn’t enabled by the`useSourceURL` test

* Optimized`isPlainObject`

* Added`callback` and`thisArg` arguments to`_.drop` and`_.pick`