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A drop-in replacement for Underscore.js that delivers performance improvements, bug fixes, and additional features.
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Lo-Dash v0.2.1

A drop-in replacement for Underscore.js, from the devs behind, that delivers performance improvements, bug fixes, and additional 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.

Dive in

We’ve got API docs and unit tests.

For a list of upcoming features, check out our roadmap.


For more information check out these screencasts over Lo-Dash:



Lo-Dash has been tested in at least Chrome 5-19, Firefox 1.5-12, IE 6-9, Opera 9.25-11.64, Safari 3.0.4-5.1.3, Node.js 0.4.8-0.6.18, 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.

Custom builds may be created in two ways:

  1. Use theinclude argument to pass the names of the methods to include in the build.
node build include=each,filter,map,noConflict
node build include="each, filter, map, noConflict"
  1. Use the exclude argument to pass the names of the methods to exclude from the build.
node build exclude=isNaN,isUndefined,union,zip
node build exclude="isNaN, isUndefined, union, zip"

Custom builds are saved to lodash.custom.js and lodash.custom.min.js.

Installation and usage

In browsers:

<script src="lodash.js"></script>

Using npm:

npm install lodash

In Node.js and RingoJS v0.8.0+:

var _ = require('lodash');

In Narwhal and RingoJS v0.7.0-:

var _ = require('lodash')._;

In Rhino:


In an AMD loader like RequireJS:

  'paths': {
    'underscore': 'path/to/lodash'
['underscore'], function(_) {

Cloning this repo

To clone this repository including all submodules, using Git 1.6.5 or later:

git clone --recursive
cd lodash.js

For older Git versions, just use:

git clone
cd lodash
git submodule update --init

Closed Underscore.js issues

  • Ensure _.groupBy adds values to own, not inherited, properties [test]
  • Ensure _.throttle works when called in tight loops [#502, test]
  • Fix Firefox, IE, Opera, and Safari object iteration bugs [#376, test, test, test, test, test, test]
  • Handle arrays with undefined values correctly in IE < 9 [#601]
  • Methods should work on pages with incorrectly shimmed native methods [#7, test]
  • Register as AMD module, but still export to global [#431, test]
  • _.forEach should be chainable [#142, test]
  • _isNaN(new Number(NaN)) should return true [test]
  • _.reduceRight should pass correct callback arguments when iterating objects [test]
  • _.size should return the length of string values [test]

Optimized methods (50+)

  • _.bind
  • _.bindAll
  • _.clone
  • _.compact
  • _.contains, _.include
  • _.defaults
  • _.defer
  • _.difference
  • _.each
  • _.escape
  • _.every, _.all
  • _.extend
  • _.filter,
  • _.find, _.detect
  • _.flatten
  • _.forEach, _.each
  • _.functions, _.methods
  • _.groupBy
  • _.indexOf
  • _.intersection
  • _.invoke
  • _.isEmpty
  • _.isEqual
  • _.isFinite
  • _.isObject
  • _.isString
  • _.keys
  • _.lastIndexOf
  •, _.collect
  • _.max
  • _.memoize
  • _.min
  • _.mixin
  • _.pick
  • _.pluck
  • _.reduce, _.foldl, _.inject
  • _.reject
  • _.result
  • _.shuffle
  • _.some, _.any
  • _.sortBy
  • _.sortedIndex
  • _.template
  • _.throttle
  • _.toArray
  • _.union
  • _.uniq, _.unique
  • _.values
  • _.without
  • _.wrap
  • plus all _(...) method wrappers



  • Adjusted the Lo-Dash export order for r.js
  • Ensured _.groupBy values are added to own, not inherited, properties
  • Made _.bind follow ES5 spec to support a popular Backbone.js pattern
  • Removed the alias intersect
  • Simplified _.bind, _.flatten, _.groupBy, _.max, and _.min


  • Added custom build options
  • Added default _.templateSettings.variable value
  • Added "lazy bind" support to _.bind
  • Added native method overwrite detection to avoid bad native shims
  • Added support for more AMD build optimizers and aliasing as the "underscore" module
  • Added thisArg argument to _.groupBy
  • Added whitespace to compiled strings
  • Added _.partial method
  • Commented the iterationFactory options object
  • Ensured _.max and _.min support extremely large arrays
  • Ensured _.throttle works in tight loops
  • Fixed IE < 9 [DontEnum] bug and Firefox < 3.6, Opera > 9.50 - Opera < 11.60, and Safari < 5.1’s prototype property iteration bug
  • Inlined _.isFunction calls.
  • Made _.debounce’ed functions match _.throttle’ed functions’ return value behavior
  • Made _.escape no longer translate the ">" character
  • Fixed clearTimeout typo
  • Simplified all methods in the "Arrays" category
  • Optimized _.debounce, _.escape, _.flatten, _.forEach, _.groupBy, _.intersection, _.invoke, _.isObject, _.max, _.min, _.pick, _.shuffle, _.sortedIndex, _.template, _.throttle, _.union, _.uniq


  • Initial release


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.



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