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
• Available on cdnjs thanks to CloudFlare
• For optimal performance, create a custom build with only the features you need

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:

• Introducing Lo-Dash
• Optimizations and custom builds
• Lo-Dash’s origin and why it’s a better utility belt

• 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 9.25-12, 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.

• Backbone builds, containing all methods required by Backbone, may be created using the backbone modifier argument.

node build backbone

• Mobile builds, with IE bug fixes and method compilation removed, may be created using the mobile modifier 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"

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

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

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

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

All arguments, except include and exlcude, may be combined.

node build backbone mobile category=functions include=pick,uniq
node build backbone mobile category=utilities exclude=first,last

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

In browsers:

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

or use the CDN:
<script src="http://cdnjs.cloudflare.com/ajax/libs/lodash.js/0.3.2/lodash.min.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);
});

• Allow iteration of objects with a length property [#148, #154, #252, #448, #659, test]
• Ensure "Arrays" category methods allow falsey array arguments [test]
• Ensure array-like objects with invalid length properties are treated like regular objects [test, test, test]
• Ensure _(…) returns passed wrapper instances [test]
• Ensure _.escape returns an empty string when passed null or undefined [#407, 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
• _.isArguments
• _.isDate
• _.isEmpty
• _.isEqual
• _.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

• Deprecated _(…).chain, _.isFinite, _.isNaN, _.isNull, _.isUndefined, _.result, and _.size
• Ensured _.escape returns an empty string when passed null or undefined
• Ensured sourceURL support doesn't cause errors in Adobe's JS engine.
• Fixed regression in generating custom builds
• Moved _.invoke and _.pluck back to the "Collections" category
• Moved _.tap to the "Chaining" category

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.

• John-David Dalton

• Kit Cambridge
• Mathias Bynens