1.0.4 • Public • Published


Asynchronous LINQ library for JavaScript, small, zero-dependency and strengthened by unit tests

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Implementation status

We keep async-linq on par with .NET version with minimal adjustments to fit JavaScript language. And referenced from Microsoft 101 LINQ Samples page.

Clauses implemented: aggregate, all, any, average, concat, count, distinct, elementAt, equalAll, except, first, firstOrDefault, groupBy, groupJoin, intersect, join, last, lastOrDefault, max, min, ofType, orderBy, orderByDescending, range, repeat, reverse, select, selectMany, skip, skipWhile, sum, take, takeWhile, thenBy, thenByDescending, toArray, toDictionary, union, where, and zip.

Beauty of async-linq

We love async, functional programming, and mixing between array + map. We want to bring LINQ to JavaScript without losing all beautiful aspects of JavaScript:

  1. Support both sync and async on every clauses.

If you are building new clauses, you only need to implement async version. All async clauses will be automatically converted to sync version. Additionally, you can implement sync version for better performance too 2. Both array and map are first-class citizen 3. Maintain code clarity by chaining clauses 4. Every clause is backed by unit tests, with over 500 unit tests passing 5. Small in size, 6 KB after gzip 6. JSHint-friendly

Before jumping in

There are some key differences between common practices of C# and JavaScript.

  1. linq([0, 1, 2]).first(function (v) { return v % 2; }) will return the index to the first odd number, i.e. 1, missing values will be returned as undefined

This is to bring clauses on map to be on-par with array. because linq({ abc: 123, def: 456, xyz: 789 }).first(...).run() should returns the name of the map, instead of value 2. Predicate signature is usually function (value, indexOrName, callback) (callback is only required for async) 3. Comparison signature is usually function (value1, indexOrName1, value2, indexOrName2, callback) 4. Selector signature is usually function (value, indexOrName, callback) 5. Callback signature is usually callback(err, result) 6. this keyword will always reference to the array/map or intermediates 7. run() is required to execute the query


To list files and their file sizes

linq(['abc.txt', 'def.txt', 'xyz.txt'])
    .select(function (filename, index, callback) {
        fs.stat(filename, function (err, stat) {
            callback(err, err ? null : {
                filename: filename,
                size: stat.size
    .run(function (err, result) {

Clauses chaining

linq([1, 2, 3, 4, 5, 6, 7, 8, 9, 0])
    .where(function (v) { return v % 2 === 1; })
    .select(function (v) { return v * 100; })

Will return [100, 300, 500, 700, 900]


Please file bugs to issues. To include your bug as regression test, you are recommended to provide a minimal failing test case.



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