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

• Development source
• Production source
• CDN copies of ≤ v0.7.0 are 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
• Lo-Dash optimizations and custom builds
• Lo-Dash’s origin and why it’s a better utility belt
• Unit testing in Lo-Dash
• Lo-Dash’s approach to native method use

• AMD loader support (RequireJS, curl.js, etc.)
• _.bind supports “lazy” binding
• _.clone supports “deep” cloning
• _.countBy as a companion function for _.groupBy and _.sortBy
• _.debounce’ed functions match _.throttle’ed functions’ return value behavior
• _.forEach is chainable and supports exiting iteration early
• _.forIn for iterating over an object’s own and inherited properties
• _.forOwn for iterating over an object’s own properties
• _.indexOf and _.lastIndexOf accept a fromIndex argument
• _.invert to create inverted objects
• _.merge for a “deep” _.extend
• _.object and _.pairs for composing objects
• _.omit for the inverse functionality of _.pick
• _.partial for partial application without this binding
• _.pick and _.omit accept callback and thisArg arguments
• _.random for generating random numbers within a given range
• _.sortBy performs a stable sort
• _.template utilizes sourceURLs for easier debugging
• _.unescape to unescape strings escaped by _.escape
• _.where for filtering collections by contained properties
• _.countBy, _.groupBy, _.sortedIndex, and _.uniq accept a thisArg argument
• _.contains, _.size, _.toArray, and more… accept strings

Lo-Dash has been tested in at least Chrome 5-21, Firefox 1-15, IE 6-9, Opera 9.25-12, Safari 3-6, Node.js 0.4.8-0.8.8, Narwhal 0.3.2, RingoJS 0.8, and Rhino 1.7RC5.

Custom builds make it easy to create lightweight versions of Lo-Dash containing only the methods you need. To top it off, we handle all method dependency and alias mapping for you.

• Backbone builds, with only 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, with iteration fixes removed and only Underscore’s API, may be created using the underscore modifier argument.

lodash underscore

Custom builds may be created using the following commands:

• Use the category argument to pass comma separated 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"

• Use the exclude argument to pass comma separated names of methods to exclude from the build.

lodash exclude=union,uniq,zip
lodash exclude="union, uniq, zip"

• Use the exports argument to pass comma separated names of ways to export the LoDash function.
  Valid exports are “amd”, “commonjs”, “global”, “node”, and “none”.

lodash exports=amd,commonjs,node
lodash include="amd, commonjs, node"

• Use the iife argument to specify code to replace the immediately-invoked function expression that wraps Lo-Dash.

lodash iife="!function(window,undefined){%output%}(this)"

• Use the include argument to pass comma separated names of methods to include in the build.

lodash include=each,filter,map
lodash include="each, filter, map"

All arguments, except exclude with include and legacy with csp/mobile, may be combined.

lodash backbone legacy exports=global category=utilities exclude=first,last
lodash -s underscore mobile strict exports=amd category=functions include=pick,uniq

The following options are also supported:

• -c, --stdout Write output to standard output
• -h, --help Display help information
• -o, --output Write output to a given path/filename
• -s, --silent Skip status updates normally logged to the console
• -V, --version Output current version of Lo-Dash

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.

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:

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 array-like objects with invalid length properties are treated like regular objects [#741, test]
• Ensure “Arrays”, “Collections”, and “Objects” methods don’t error when passed falsey arguments [#650, test]
• Ensure “Collections” methods allow string collection arguments [#247, #276, #561, test]
• Fix cross-browser object iteration bugs [#60, #376, test]
• Methods should work on pages with incorrectly shimmed native methods [#7, #742, test]
• Register as an AMD module, but still export to global [#431, test]
• _.clone should allow deep cloning [#595, test]
• _.contains should work with strings [#667, test]
• _.countBy and _.groupBy should only add values to own, not inherited, properties [#736, test]
• _.extend should recursively extend objects [#379, #718, test]
• _.forEach should be chainable [#142, test]
• _.forEach should allow exiting iteration early [#211, test]
• _.isElement should use strict equality for its duck type check [#734, test]
• _.isEmpty should support jQuery/MooTools DOM query collections [#690, test]
• _.isEqual should return true for like-objects from different documents [#733, test]
• _.isEqual should use custom isEqual methods before checking strict equality [#748, test]
• _.isObject should avoid V8 bug #2291 [#605, test]
• _.isNaN(new Number(NaN)) should return true [#749, test]
• _.keys should work with arguments objects cross-browser [#396, test]
• _.range should coerce arguments to numbers [#634, #683, test]
• _.reduceRight should pass correct callback arguments when iterating objects [test]
• _.sortedIndex should support arrays with high length values [#735, test]
• _.throttle should work when called in a loop [#502, test]
• _.toArray uses custom toArray methods of arrays and strings [#747, test]

• _.bind
• _.bindAll
• _.clone
• _.compact
• _.contains, _.include
• _.defaults
• _.defer
• _.difference
• _.each
• _.every, _.all
• _.extend
• _.filter, _.select
• _.find, _.detect
• _.flatten
• _.forEach, _.each
• _.functions, _.methods
• _.groupBy
• _.indexOf
• _.intersection
• _.invert
• _.invoke
• _.isArguments
• _.isDate
• _.isEmpty
• _.isFinite
• _.isFunction
• _.isObject
• _.isNumber
• _.isRegExp
• _.isString
• _.keys
• _.lastIndexOf
• _.map, _.collect
• _.max
• _.memoize
• _.min
• _.mixin
• _.omit
• _.pairs
• _.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

• Renamed _.zipObject to _.object
• Replaced _.drop with _.omit
• Made _.drop alias _.rest

• Added _.invert, _.pairs, and _.random
• Added _.result to the backbone build
• Added exports, iife, -c/--stdout, -o/--output, and -s/--silent build options
• Ensured isPlainObject works with objects from other documements
• Ensured _.isEqual compares values with circular references correctly
• Ensured _.merge work with four or more arguments
• Ensured _.sortBy performs a stable sort for undefined values
• Ensured _.template works with "interpolate" delimiters containing ternary operators
• Ensured the production build works in Node.js
• Ensured template delimiters are tokenized correctly
• Made pseudo private properties _chain and _wrapped double-underscored to avoid conflicts
• Made minify.js support underscore.js
• Reduced the size of mobile and underscore builds
• Simplified _.isEqual and _.size

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