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Lo-Dash v0.5.1

A drop-in replacement* for Underscore.js, from the devs behind, delivering performance, 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, benchmarks, and unit tests.

Create your own benchmarks at jsPerf, or search for existing ones.

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 5-21, Firefox 1.5-13, IE 6-9, Opera 9.25-12.01, Safari 3-6, Node.js 0.4.8-0.8.7, Narwhal 0.3.2, RingoJS 0.8, and Rhino 1.7RC5.

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.
lodash backbone
  • CSP builds, supporting default Content Security Policy restrictions, may be created using the csp modifier argument.
lodash csp
  • Legacy builds, tailored for older browsers without ES5 support, may be created using the legacy modifier argument.
lodash legacy
  • Mobile builds, with IE < 9 bug fixes and method compilation removed, may be created using the mobile modifier argument.
lodash mobile
  • Strict builds, with _.bindAll, _.defaults, and _.extend in strict mode, may be created using the strict modifier argument.
lodash strict
  • Underscore builds, containing only methods included in Underscore, may be created using the underscore modifier argument.
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".
lodash category=collections,functions
lodash category="collections, functions"
  1. Use the exclude argument to pass the names of methods to exclude from the build.
lodash exclude=union,uniq,zip
lodash exclude="union, uniq, zip"
  1. Use the include argument to pass the names of methods to include in the build.
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.

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:

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

Using npm:

npm install lodash
npm install -g lodash

In Node.js and RingoJS v0.8.0+:

var _ = require('lodash');

In RingoJS v0.7.0-:

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

In Rhino:


In an AMD loader like RequireJS:

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

Resolved Underscore.js issues (20+)

  • Allow iteration of objects with a length property [#148, #154, #252, #448, #659, test]
  • Ensure array-like objects with invalid length properties are treated like regular objects [test]
  • Ensure "Arrays" methods allow falsey array arguments [test]
  • Ensure "Collections" methods allow string collection arguments [#247, #276, #561, test]
  • Ensure templates compiled with errors are inspectable [#666, test]
  • Fix cross-browser object iteration bugs [#60, #376, 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 an AMD module, but still export to global [#431, test]
  • _(…) should return passed wrapper instances [test]
  • _.clone should allow deep cloning [#595, test]
  • _.contains should work with strings [#667, test]
  • _.escape should return an empty string when passed null or undefined [#427, test]
  • _.extend should recursively extend objects [#379, test]
  • _.forEach should be chainable [#142, test]
  • _.forEach should allow exiting iteration early [#211, test]
  • _.groupBy should add values to own, not inherited, properties [test]
  • _.isEmpty and _.size should support jQuery/MooTools DOM query collections [#690, test]
  • _.isEqual should return true for like-objects from different documents [test]
  • _.isObject should avoid V8 bug #2291 [#605, test]
  • _.isNaN(new Number(NaN)) should return true [test]
  • _.keys and _.size should work with arguments objects cross-browser [#396, #653, test]
  • _.once should free the given function for garbage collection [#693]
  • _.range should coerce arguments to numbers [#634, #683, test]
  • _.reduceRight should pass correct callback arguments when iterating objects [test]
  • _.size should return the length of string values [test]
  • _.size shouldn’t error on falsey values [#650, test]
  • _.sortedIndex should support arrays with high length values [test]
  • _.template should not augment the options object [test]
  • _.throttle should work when called in a loop [#502, test]
  • _.zipObject should accept less than two arguments [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
  • _.isArguments
  • _.isDate
  • _.isEmpty
  • _.isFinite
  • _.isFunction
  • _.isObject
  • _.isNumber
  • _.isRegExp
  • _.isString
  • _.keys
  • _.lastIndexOf
  •, _.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
  • plus all _(…) method wrappers

Release Notes


  • Ensured _.bind correctly appends array arguments to partially applied arguments in older browsers


  • Added _.countBy, _.drop, _.merge, and _.where
  • Added csp (Content Security Policy) and underscore build options
  • Added deep cloning support to _.clone
  • Added Jam package support
  • Added support for exiting _.forEach, _.forIn, and _.forOwn early by returning false in the callback
  • Added support for jQuery/MooTools DOM query collections to _.isEmpty and _.size
  • 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 _.once frees the given function for garbage collection
  • Ensured _.sortBy performs a stable sort
  • Ensured reEvaluateDelimiter is assigned when _.templateSettings.evaluate is undefined
  • Made _.range coerce arguments to numbers
  • Optimized _.isFunction

The full changelog is available here.


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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