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MAJOR UPDATE: I've rewritten the entire thing into linqer-ts. Any improvements or updates will be on that project.


The C# Language Integrated Queries ported for Javascript for amazing performance

npm version License: MIT


$ npm install @siderite/linqer

Quick start

const source = ... an array or a generator function or anything that is iterable... ;
const enumerable = Linqer.Enumerable.from(source); // now you can both iterate and use LINQ like functions
const result = enumerable
                .where(item=>!!item.value) // like filter
                .select(item=>{ value: item.value, key: }) // like map
for (const item of result) ...

in Node.js you have to prepend:

const Linqer = require('@siderite/linqer');

in Typescript, use the .ts files directly or install @types/node and use require, I guess. I couldn't make it work for both TS and JS. I will try to make that happen in version 2, which will probably have a different file layout.



Array functions in Javascript create a new array for each operation, which is terribly wasteful. Using iterators and generator functions and objects, we can limit the operations to the items in the array that interest us, not all of them.

Blog post Leave comments there or add Issues on GitHub for feedback and support.


Find it hosted on GitHub Pages and use it freely in your projects at:


Reference Linqer.slim.js for the basic methods:

  • from, empty, range, repeat - static on Linqer.Enumerable
  • length property - same as count, but throws error if the enumerable needs to be enumerated to get the length (no side effects)
  • concat
  • count
  • distinct
  • elementAt and elementAtOrDefault
  • first and firstOrDefault
  • last and lastOrDefault
  • min, max, stats (min, max and count)
  • select
  • skip and take
  • splice function - kind of useless, but it was an experiment to see if I can make Enumerable appear as an Array-like object
  • sum and sumAndCount (sum and count)
  • toArray
  • toList - similar to toArray, but returns a seekable Enumerable (itself if already seekable) that can do count and elementAt without iterating
  • where

Reference Linqer.js for all of the original Enumerable methods, the ones in slim and then the following:

  • aggregate
  • all
  • any
  • append
  • average
  • asEnumerable
  • cast
  • contains
  • defaultIfEmpty - throws not implemented
  • except
  • intersect
  • join
  • groupBy
  • groupJoin
  • longCount
  • ofType
  • orderBy
  • orderByDescending
  • prepend
  • reverse
  • selectMany
  • sequenceEqual
  • single
  • singleOrDefault
  • skip - on an ordered enumerable
  • skipLast - on a regular or ordered enumerable
  • skipWhile
  • slice
  • take - on an ordered enumerable
  • takeLast - on a regular or ordered enumerable
  • takeWhile
  • thenBy - on an ordered enumerable
  • thenByDescending - on an ordered enumerable
  • toDictionary - throws not implemented
  • toLookup - throws not implemented
  • toMap
  • toObject
  • toHashSet - throws not implemented
  • toSet
  • union
  • zip

Reference Linqer.extra.js (needs Linqer.js) for some additional methods:

  • shuffle - randomizes the enumerable
  • randomSample - implements random reservoir sampling of k items
  • distinctByHash - distinct based on a hashing function, not a comparer - faster
  • exceptByHash - except based on a hashing function, not a comparer - faster
  • intersectByHash - intersect based on a hashing function, not a comparer - faster
  • binarySearch - find the index of a value in a sorted enumerable by binary search
  • lag - joins each item of the enumerable with previous items from the same enumerable
  • lead - joins each item of the enumerable with next items from the same enumerable
  • padStart - pad enumerable at the start to a minimum length
  • padEnd - pad enumerable at the end to a minimum length

Original Enumerable .NET class

The original C# class can be found here: .

Building the solution

The library has been ported to Typescript. Run build.bat to create the .js and .map files from the .ts code.


The C# Language Integrated Queries ported for Javascript for amazing performance







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