I wanted to add this document because it is not clear why some methods are accepted as filter and why some are not. I am trying to define quidelines over here and analyze all LoDash methods and point out why some method is or is not accepted.
First of all AngularJS Filter developer guide states that:
A filter formats the value of an expression for display to the user. They can be used in view templates, controllers or services and it is easy to define your own filter.
Ok, now let's start discussion of the rulez!
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Selected method cannot alter the original value. This means that it is not allowed to remove any values from original Array or Object. It also cannot change the original String or Number in anyways.
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They can be used in view templates, controllers or services..., when we start to thinking about this, we should remember that
ropooy-angular-rdashis providing service_, which can be injected in to Service, Controller, Directive and Filter.Example below shows the ways how you can currently use LoDash functions inside Service, Controller, Directive or Filter. If you ask from me, I would use service
_instead of any other ways. (less writing)//simplified controller... function($scope, $filter, _) { // as util var way1 = $scope.uniq([1, 2, 1]); // as filter var way2 = $filter('uniq')([1, 2, 1]); // as DI service var way3 = _.uniq([1, 2, 1]); }
... and from that we should only think if some LoDash method is suitable as filter inside view template.
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Now, what means suitable as filter? Next example demostrates one crazy way. Lets asume that we have added isEmpty as filter, it returns a Boolean value. We need to remember from last example that $scope contains also 'isEmpty()' -method.
//simplified controller function myCtrl($scope) { $scope.foo = []; }
<div ng-controller="myCtrl"> <!-- would you use isEmpty() as utility? --> <p ng-if="isEmpty(foo);">Foo is empty</p> <!-- or would you like to use it as filter? I doubt it.--> <p ng-if="'{{foo |isEmpty}}'">Foo is empty</p> </div>
Guideline summary:
- It cannot alter the original value.
- Its usage must be reasonable inside view tempalte (it returns Array, Object, String or Number)
chunk,compact,difference,drop,dropRight,dropRightWhile,dropWhile,flatten,flattenDeep,initial,intersection,rest and tail,slice,take,takeRight,takeRightWhile,takeWhile,union,uniq and unique,unzip,unzipWith,without,xor,zipandzipWith- returns Array, usable inng-repeat.
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findIndex,findLastIndex,indexOf,lastIndexOf,sortedIndex,sortedLastIndex- retuns index of the found element, else -1. Cannot see any valid use case in view template atm. -
pull,pullAtandremove- removes elements from the original array. -
fill- returns Array, but more usable as utility. -
first and head,last,zipObject and object- more usable as utility.<button ng-click="ziped = zipObject(['fred', 'barney'],[30, 40])"> {{ziped.fred || 'No value'}} </button>
- --all--
at,filter and select,map and collect,pluck,reject,sample,shuffle,sortBy,sortByAll,sortByOrder,where,invoke,partition,reduce, foldl and inject,reduceRight and foldr- returns Array, usable inng-repeatfind and detect,findLast,findWhere- usable, depending what is the returned element.countBy,groupBy,indexBy- returns the composed aggregate object. This is more usable as utility instead of inside view assignment, but this could be used in filter chain.
every and all,includes, contains and include,some and any- retuns Boolean, more usable as utility.size- returns Number, more usable as utility.forEach and each,forEachRight andeachRight` - returns Array, but more usable as utility.
- --none--
now- usable as utility.
- --none--
after,bind,bindAll,bindKey,compose,curry,debounce,defer,delay,memoize,once,partial,partialRight,throttle,wrap- cannot see any sensible use cases atm.
toArray- returns Array, usable inng-repeat
clone,cloneDeep,gt,gte,isArguments,isArray,isBoolean,isDate,isElement,isEmpty,isEqual,isError,isFinite,isFunction,isNaN,isNative,isNull,isNumber,isObject,isPlainObject,isRegExp,isString,isTypedArray,isUndefined,lg,lte- returns Boolean, more usable as utility.toPlainObject- retuns the converted plain object, usable as utility.
add,ceil,floor,max,min,round,sum- all work nicely as filter.
- --none--
- --none--
inRange- returns Boolean, usable as utility.random- returns Number, usable as utility.
functions and methods,keys,keysIn,merge,pairs,values,valuesIn- usable inng-repeatget,result- looks nice filter.invert,mapKeys,mapValues,omit,pick- Returns object.transform- return the accumulated value.
assign and extend, ,create,defaults,defaultsDeep,findKey,findLastKey,forIn,forInRight,forOwn,forOwnRight- These are more like utility.has- returns Boolean, more usable as utility.set- adds property / value -> manipulates original.transform- returns the accumulated value. TODO: Need good use case, without utility possibility.
camelCase,capitalize,deburr,escape,escapeRegExp,kebabCase,pad,padLeft,padRight,repeat,snakeCase,startCase,trim,trimLeft,trimRight,trunc,unescape- returns String.parseInt- returns Number.words- returns Array, usable inng-repeat.
template- usable as utility.endsWith,startsWith- returns Boolean, usable as utility.
uniqueId- returns String.result- returns resolved value.times- returns Array.
attempt,callback and iteratee,constant,identity,matches,matchesProperty,method,methodOf,mixin,noConflict,noop,property,propertyOf,range,runinContext- these are utility.
- Second iteration was a bit easier. Added more consistency to methods which returns Array or Object.
- I also got stronger feeling that are you benefitting at all if you are using filters and utilities? I think that you are using either filters or utils. Good filters would be some composition methods / mixins which you are creating specifically to filter data in your service. Plain LoDash methods work in the same way whether you are using filter or util.
- We should also have a list of the methods which work as utility inside view template. Example
forEachis not very useful inside view template, butisXYZmethods are. Current 3.10.1 LoDash version has 219 methods, which are currently added into$scopeif you are using utils.