A drop-in replacement for Underscore.js, from the devs behind jsPerf.com, 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.

• Development source
• Production source
• For optimal performance, create a custom build with only the features you need

We’ve got API docs, benchmarks, and unit tests.

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

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

• Introducing Lo-Dash
• Optimizations and custom builds

• AMD loader support (RequireJS, curl.js, etc.)
• _.bind supports "lazy" binding
• _.debounce’ed functions match _.throttle’ed functions’ return value behavior
• _.forEach is chainable
• _.forIn for iterating over an object’s own and inherited properties
• _.forOwn for iterating over an object’s own properties
• _.groupBy, _.sortedIndex, and _.uniq accept a thisArg argument
• _.indexOf and _.lastIndexOf accept a fromIndex argument
• _.partial for more functional fun
• _.size supports returning the length of string values
• _.template utilizes sourceURLs for easier debugging

Lo-Dash has been tested in at least Chrome 5-19, Firefox 1.5-13, 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 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.

Mobile builds, with IE bug fixes and method compilation removed, may be created by using the mobile argument.

node build mobile

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".

node build category=collections,functions
node build category="collections, functions"
node build mobile category=collections,functions

2. Use the include argument to pass the names of the methods to include in the build.

node build include=each,filter,map
node build include="each, filter, map"
node build mobile include=each,filter,map

3. Use the exclude argument to pass the names of the methods to exclude from the build.

node build exclude=union,uniq,zip
node build exclude="union, uniq, zip"
node build mobile exclude=union,uniq,zip

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

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:

load('lodash.js');

In an AMD loader like RequireJS:

require({
  'paths': {
    'underscore': 'path/to/lodash'
  }
},
['underscore'], function(_) {
  console.log(_.VERSION);
});

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

git clone --recursive https://github.com/bestiejs/lodash.git
cd lodash.js

For older Git versions, just use:

git clone https://github.com/bestiejs/lodash.git
cd lodash
git submodule update --init

• Allow iteration of objects with a length property [#148, #154, #252, #448, test]
• Ensure array-like objects with invalid length properties are treated like regular objects [test, test, test]
• Ensure _(...) returns passed wrapper instances [test]
• Ensure _.groupBy adds values to own, not inherited, properties [test]
• Ensure _.sortedIndex supports arrays with high length values [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]

• _.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
• _.isEmpty
• _.isEqual
• _.isFinite
• _.isObject
• _.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

• Added category build option
• Added fromIndex argument to _.indexOf and _.lastIndexOf
• Added //@ sourceURL support to _.template
• Added thisArg argument to _.sortedIndex and _.uniq
• Added _.forIn and _.forOwn methods
• Ensured array-like objects with invalid length properties are treated like regular objects
• Ensured _.sortedIndex supports arrays with high length values
• Fixed prototype property iteration bug in _.keys for Firefox < 3.6, Opera > 9.50 - Opera < 11.60, and Safari < 5.1
• Optimized _.times and this bindings in iterator methods

• Added mobile build option
• Ensured _.find returns undefined for unmatched values
• Ensured _.templateSettings.variable is compatible with Underscore.js
• Optimized _.escape
• Reduced dependencies in _.find

• 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 _(...) returns passed wrapper instances
• 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.

• John-David Dalton

• Kit Cambridge
• Mathias Bynens