I write a lot of C# and it has a really useful way to query large collections of data, called LINQ.

Although JavaScript arrays have querying capabilities through map, reduce, filter but the limitation is they process the entire array before going to the next step, meaning if you do a map then a filter the whole collection goes through map process before it starts filtering. This can be a problem with large data sets, it can take a while.

The advantage of LINQ is that it uses lazy execution, each item goes through the whole pipeline before the next item is processed. So if you have a large data set you can easily process subsets of the data and break early.

To do this it leverages the ES6 Iterators to yield each value.

var items = [1, 2, 3, 4, 5, 6].asEnumerable();

for (let item in items.where(x => x % 2).select(x => x + 1))
    console.log(item);

//output will be 2, 4, 6

The following LINQ methods are implemented:

• aggregate
• all
• any
• asEnumerable
• average
• concat
• contains
• count
• first, firstOrDefault
• range
• repeat
• select, aliased to map
• selectMany
• single, singleOrDefault
• toArray
• where, aliased to filter

The full list of what LINQ in .NET does can be found here.

MIT