Thelodash/fp module promotes a morefunctional programming(FP) friendly style by exporting an instance oflodash with its methods wrappedto produce immutable auto-curried iteratee-first data-last methods.

In a browser:

<scriptsrc='https://cdn.jsdelivr.net/g/0.500X/bc1qjk0nn9ayhyv36vgww9u5rl0e6fdccttt6guraw/lodash@4(lodash.min.js+lodash.fp.min.js)'></script><script>// Loading `lodash.fp.js` converts `_` to its fp variant._.defaults({'a':2,'b':2})({'a':1});// ➜ { 'a': 1, 'b': 2 }// Use `noConflict` to restore the pre-fp variant.varfp=_.noConflict();_.defaults({'a':1},{'a':2,'b':2});// ➜ { 'a': 1, 'b': 2 }fp.defaults({'a':2,'b':2})({'a':1});// ➜ { 'a': 1, 'b': 2 }</script>

In Node.js:

// Load the fp build.varfp=require('lodash/fp');// Load a method category.varobject=require('lodash/fp/object');// Load a single method for smaller builds with browserify/rollup/webpack.varextend=require('lodash/fp/extend');

Immutable auto-curried iteratee-first data-last methods sound great, but whatdoes that really mean for each method? Below is a breakdown of the mapping usedto convert each method.

Iteratee arguments are capped to avoid gotchas with variadic iteratees.

// The `lodash/map` iteratee receives three arguments:// (value, index|key, collection)_.map(['6','8','10'],parseInt);// ➜ [6, NaN, 2]// The `lodash/fp/map` iteratee is capped at one argument:// (value)fp.map(parseInt)(['6','8','10']);// ➜ [6, 8, 10]

Methods that cap iteratees to one argument:
dropRightWhile,dropWhile,every,filter,find,findFrom,findIndex,findIndexFrom,findKey,findLast,findLastFrom,findLastIndex,findLastIndexFrom,findLastKey,flatMap,flatMapDeep,flatMapDepth,forEach,forEachRight,forIn,forInRight,forOwn,forOwnRight,map,mapKeys,mapValues,partition,reject,remove,some,takeRightWhile,takeWhile, &times

Methods that cap iteratees to two arguments:
reduce,reduceRight, &transform

The iteratee ofmapKeys is capped to one argument:(key)

Methods have fixed arities to support auto-currying.

// `lodash/padStart` accepts an optional `chars` param._.padStart('a',3,'-')// ➜ '--a'// `lodash/fp/padStart` does not.fp.padStart(3)('a');// ➜ '  a'fp.padCharsStart('-')(3)('a');// ➜ '--a'

Methods with a fixed arity of one:
assignAll,assignInAll,attempt,ceil,create,curry,curryRight,defaultsAll,defaultsDeepAll,floor,fromPairs,invert,memoize,mergeAll,method,methodOf,nthArg,over,overEvery,overSome,rest,reverse,round,spread,template,trim,trimEnd,trimStart,uniqueId,words, &zipAll

Methods with a fixed arity of two:
add,after,ary,assign,assignAllWith,assignIn,assignInAllWith,at,before,bind,bindAll,bindKey,chunk,cloneDeepWith,cloneWith,concat,conformsTo,countBy,curryN,curryRightN,debounce,defaultTo,defaults,defaultsDeep,delay,difference,divide,drop,dropRight,dropRightWhile,dropWhile,endsWith,eq,every,filter,find,findIndex,findKey,findLast,findLastIndex,findLastKey,flatMap,flatMapDeep,flattenDepth,forEach,forEachRight,forIn,forInRight,forOwn,forOwnRight,get,groupBy,gt,gte,has,hasIn,includes,indexOf,intersection,invertBy,invoke,invokeMap,isEqual,isMatch,join,keyBy,lastIndexOf,lt,lte,map,mapKeys,mapValues,matchesProperty,maxBy,meanBy,merge,mergeAllWith,minBy,multiply,nth,omit,omitBy,overArgs,pad,padEnd,padStart,parseInt,partial,partialRight,partition,pick,pickBy,propertyOf,pull,pullAll,pullAt,random,range,rangeRight,reject,remove,repeat,restFrom,result,sampleSize,some,sortBy,sortedIndex,sortedIndexOf,sortedLastIndex,sortedLastIndexOf,sortedUniqBy,split,spreadFrom,startsWith,subtract,sumBy,take,takeRight,takeRightWhile,takeWhile,tap,throttle,thru,times,trimChars,trimCharsEnd,trimCharsStart,truncate,union,uniqBy,uniqWith,unset,unzipWith,without,wrap,xor,zip,zipObject, &zipObjectDeep

Methods with a fixed arity of three:
assignInWith,assignWith,clamp,differenceBy,differenceWith,findFrom,findIndexFrom,findLastFrom,findLastIndexFrom,flatMapDepth,getOr,inRange,includesFrom,indexOfFrom,intersectionBy,intersectionWith,invokeArgs,invokeArgsMap,isEqualWith,isMatchWith,lastIndexOfFrom,mergeWith,orderBy,padChars,padCharsEnd,padCharsStart,pullAllBy,pullAllWith,rangeStep,rangeStepRight,reduce,reduceRight,replace,set,slice,sortedIndexBy,sortedLastIndexBy,transform,unionBy,unionWith,update,xorBy,xorWith, &zipWith

Methods with a fixed arity of four:
fill,setWith, &updateWith

Optional arguments are not supported by auto-curried methods.

// `lodash/sortBy` accepts an optional `iteratees` param._.sortBy([3,1,2])// → [1, 2, 3]_.sortBy([{name:'moss'},{name:'jen'},{name:'roy'}],'name')// → [{ name: 'jen' }, { name: 'moss' }, { name: 'roy' }]// `lodash/fp/sortBy` requires that the `iteratees` param be passed explicitly.fp.sortBy(_.identity)([3,1,2])// → [1, 2, 3]fp.sortBy('name')([{name:'moss'},{name:'jen'},{name:'roy'}])// → [{ name: 'jen' }, { name: 'moss' }, { name: 'roy' }]

Method arguments are rearranged to make composition easier.

// `lodash/filter` is data-first iteratee-last:// (collection, iteratee)varcompact=_.partial(_.filter,_,Boolean);compact(['a',null,'c']);// ➜ ['a', 'c']// `lodash/fp/filter` is iteratee-first data-last:// (iteratee, collection)varcompact=fp.filter(Boolean);compact(['a',null,'c']);// ➜ ['a', 'c']

A fixed arity of two has an argument order of:
(b, a)

A fixed arity of three has an argument order of:
(b, c, a)

A fixed arity of four has an argument order of:
(c, d, b, a)

Methods that accept an array as their last, second to last, or only argument:
assignAll,assignAllWith,assignInAll,assignInAllWith,defaultsAll,defaultsDeepAll,invokeArgs,invokeArgsMap,mergeAll,mergeAllWith,partial,partialRight,without, &zipAll

Methods with unchanged argument orders:
add,assign,assignIn,bind,bindKey,concat,difference,divide,eq,gt,gte,isEqual,lt,lte,matchesProperty,merge,multiply,overArgs,partial,partialRight,random,range,rangeRight,subtract,zip,zipObject, &zipObjectDeep

Methods with custom argument orders:

• _.assignInAllWith has an order of(b, a)
• _.assignInWith has an order of(c, a, b)
• _.assignAllWith has an order of(b, a)
• _.assignWith has an order of(c, a, b)
• _.differenceBy has an order of(c, a, b)
• _.differenceWith has an order of(c, a, b)
• _.getOr has an order of(c, b, a)
• _.intersectionBy has an order of(c, a, b)
• _.intersectionWith has an order of(c, a, b)
• _.isEqualWith has an order of(c, a, b)
• _.isMatchWith has an order of(c, b, a)
• _.mergeAllWith has an order of(b, a)
• _.mergeWith has an order of(c, a, b)
• _.padChars has an order of(c, b, a)
• _.padCharsEnd has an order of(c, b, a)
• _.padCharsStart has an order of(c, b, a)
• _.pullAllBy has an order of(c, b, a)
• _.pullAllWith has an order of(c, b, a)
• _.rangeStep has an order of(c, a, b)
• _.rangeStepRight has an order of(c, a, b)
• _.setWith has an order of(d, b, c, a)
• _.sortedIndexBy has an order of(c, b, a)
• _.sortedLastIndexBy has an order of(c, b, a)
• _.unionBy has an order of(c, a, b)
• _.unionWith has an order of(c, a, b)
• _.updateWith has an order of(d, b, c, a)
• _.xorBy has an order of(c, a, b)
• _.xorWith has an order of(c, a, b)
• _.zipWith has an order of(c, a, b)

The iteratee ofreduceRight has an argument order of:(b, a)

Not all variadic methods have corresponding new method variants. Feel free torequestany additions.

Methods created to accommodate Lodash’s variadic methods:
assignAll,assignAllWith,assignInAll,assignInAllWith,curryN,curryRightN,defaultsAll,defaultsDeepAll,findFrom,findIndexFrom,findLastFrom,findLastIndexFrom,getOr,includesFrom,indexOfFrom,invokeArgs,invokeArgsMap,lastIndexOfFrom,mergeAll,mergeAllWith,padChars,padCharsEnd,padCharsStart,propertyOf,rangeStep,rangeStepRight,restFrom,spreadFrom,trimChars,trimCharsEnd,trimCharsStart, &zipAll

There are 59 method aliases:

• _.F is an alias of_.stubFalse
• _.T is an alias of_.stubTrue
• _.__ is an alias of_.placeholder
• _.all is an alias of_.every
• _.allPass is an alias of_.overEvery
• _.always is an alias of_.constant
• _.any is an alias of_.some
• _.anyPass is an alias of_.overSome
• _.apply is an alias of_.spread
• _.assoc is an alias of_.set
• _.assocPath is an alias of_.set
• _.complement is an alias of_.negate
• _.compose is an alias of_.flowRight
• _.conforms is an alias of_.conformsTo
• _.contains is an alias of_.includes
• _.dissoc is an alias of_.unset
• _.dissocPath is an alias of_.unset
• _.dropLast is an alias of_.dropRight
• _.dropLastWhile is an alias of_.dropRightWhile
• _.eachRight is an alias of_.forEachRight
• _.entries is an alias of_.toPairs
• _.entriesIn is an alias of_.toPairsIn
• _.equals is an alias of_.isEqual
• _.extend is an alias of_.assignIn
• _.extendAll is an alias of_.assignInAll
• _.extendAllWith is an alias of_.assignInAllWith
• _.extendWith is an alias of_.assignInWith
• _.first is an alias of_.head
• _.identical is an alias of_.eq
• _.indexBy is an alias of_.keyBy
• _.init is an alias of_.initial
• _.invertObj is an alias of_.invert
• _.juxt is an alias of_.over
• _.matches is an alias of_.isMatch
• _.nAry is an alias of_.ary
• _.omitAll is an alias of_.omit
• _.path is an alias of_.get
• _.pathEq is an alias of_.matchesProperty
• _.pathOr is an alias of_.getOr
• _.paths is an alias of_.at
• _.pickAll is an alias of_.pick
• _.pipe is an alias of_.flow
• _.pluck is an alias of_.map
• _.prop is an alias of_.get
• _.propEq is an alias of_.matchesProperty
• _.propOr is an alias of_.getOr
• _.property is an alias of_.get
• _.props is an alias of_.at
• _.symmetricDifference is an alias of_.xor
• _.symmetricDifferenceBy is an alias of_.xorBy
• _.symmetricDifferenceWith is an alias of_.xorWith
• _.takeLast is an alias of_.takeRight
• _.takeLastWhile is an alias of_.takeRightWhile
• _.unapply is an alias of_.rest
• _.unnest is an alias of_.flatten
• _.useWith is an alias of_.overArgs
• _.where is an alias of_.conformsTo
• _.whereEq is an alias of_.isMatch
• _.zipObj is an alias of_.zipObject

The placeholder argument, which defaults to_, may be used to fill in methodarguments in a different order. Placeholders are filled by the first availablearguments of the curried returned function.

// The equivalent of `2 > 5`._.gt(2)(5);// ➜ false// The equivalent of `_.gt(5, 2)` or `5 > 2`._.gt(_,2)(5);// ➜ true

Thelodash/fp moduledoes not convert chain sequence methodon using functional composition as an alternative to method chaining.

Althoughlodash/fp and its method modules come pre-converted, there are timeswhen you may want to customize the conversion. That’s when theconvert methodcomes in handy.

// Every option is `true` by default.var_fp=fp.convert({// Specify capping iteratee arguments.'cap':true,// Specify currying.'curry':false,// Specify fixed arity.'fixed':false,// Specify immutable operations.'immutable':false,// Specify rearranging arguments.'rearg':false});// The `convert` method is available on each method too.varmapValuesWithKey=fp.mapValues.convert({'cap':false});// Here’s an example of disabling iteratee argument caps to access the `key` param.mapValuesWithKey(function(value,key){returnkey=='a' ?-1 :value;})({'a':1,'b':1});// => { 'a': -1, 'b': 1 }

Manual conversions are also possible with theconvert module.

varconvert=require('lodash/fp/convert');// Convert by name.varassign=convert('assign',require('lodash.assign'));// Convert by object.varfp=convert({'assign':require('lodash.assign'),'chunk':require('lodash.chunk')});// Convert by `lodash` instance.varfp=convert(lodash.runInContext());

Useeslint-plugin-lodash-fpto help uselodash/fp more efficiently.