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The Interactive Extensions for JavaScript (IxJS)...

...is a set of libraries to compose synchronous and asynchronous collections and Array#extras style composition in JavaScript

The Interactive Extensions for JavaScript (IxJS) brings the Array#extras combinators to iterables, generators, async iterables and async generators. With the introduction of the Symbol.iterator and generators in ES2015, and subsequent introduction of Symbol.asyncIterator and async generators, it became obvious we need an abstraction over these data structures for composition, querying and more.

IxJS unifies both synchronous and asynchronous pull-based collections, just as RxJS unified the world of push-based collections. RxJS is great for event-based workflows where the data can be pushed at the rate of the producer, however, IxJS is great at I/O operations where you as the consumer can pull the data when you are ready.

Install IxJS from npm

npm install ix

(also read about how we package IxJS below)

Iterable

The Iterable class a way to create and compose synchronous collections much like Arrays, Maps and Sets in JavaScript using the Array#extras style using the familiar methods you are used to like map, filter, reduce and more.

// ES 
import * as Ix from 'ix';
 
// CommonJS 
const Ix = require('ix');
 
Ix.Iterable.from([1,2,3,4])
  .filter(x => x % 2 === 0)
  .map(x => x * 2)
  .forEach(x => console.log(`Next ${x}`));
 
// => 4 
// => 8 

Alternatively, we can use the for ... of statements to iterate our collections.

// ES 
import * as Ix from 'ix';
 
// CommonJS 
const Ix = require('ix');
 
const results = Ix.Iterable.from([1,2,3,4])
  .filter(x => x % 2 === 0)
  .map(x => x * 2);
 
for (let item of results) {
  console.log(`Next ${x}`);
}
 
// => 4 
// => 8 

Instead of bringing in the entire library for Iterable, we can pick and choose which operators we want, for bundling concerns.

// ES 
import { IterableX as Iterable } from 'ix/iterable';
import 'ix/add/iterable/of';
import 'ix/add/iterable-operators/map';
 
// CommonJS 
const Iterable = require('ix/iterable').IterableX;
require('ix/add/iterable/of');
require('ix/add/iterable-operators/map');
 
const results = Iterable.of(1,2,3)
  .map(x => x + '!!');

We can also bring in only the operators that we want to using just the operators themselves. Many of these operators take a simple Iterable source such as an Array, Map, Set or generator function such as our map and filter functions.

// ES 
import { map } from 'ix/iterable/map';
import { filter } from 'ix/iterable/filter';
 
// CommonJS 
const map = require('ix/iterable/map').map;
const filters = require('ix/iterable/filter').filter;
 
const source = [1,2,3];
const results = map(
  filter(
    source, 
    x => x % 2 === 0
  ),
  x => x * x
);
 
for (let item of results) {
  console.log(`Next: ${item}`);
}

We can mix the two approaches by adding the minimal chain operator which then allows us to create a more fluent style but yet keeping the surface area to a minimum.

// ES 
import { IterableX as Iterable } from 'ix/iterable';
import 'ix/add/iterable-operators/chain';
import { of } from 'ix/iterable/of';
import { filter } from 'ix/iterable/filter';
import { map } from 'ix/iterable/map';
 
// CommonJS 
const Iterable = require('ix/iterable').IterableX;
require('ix/add/iterable-operators/chain');
const of = require('ix/iterable/of');
const filter = require('ix/iterable/filter');
const map = require('ix/iterable/map');
 
const results = of(1, 2, 3)
  .chain(source => filter(source, x => x % 2 === 0))
  .chain(source => map(source, x => x * x));
 
for (let item of results) {
  console.log(`Next: ${item}`);
}

The Iterable object implements the iterator pattern in JavaScript by exposing the [Symbol.iterator] method which in turn exposes the Iterator class. The iterator yields values by calling the next() method which returns the IteratorResult class.

interface Iterable<T> {
  [Symbol.iterator](): Iterator<T>;
}
 
interface Iterator<T> {
  next(value?: any): IteratorResult<T>;
  return?(value?: any): IteratorResult<T>;
  throw?(e?: any): IteratorResult<T>;
}
 
interface IteratorResult<T> {
  value: T;
  done: Boolean;
}

AsyncIterable

The AsyncIterable object is based off the ECMAScript Proposal for Asynchronous Iterators. This would allow us to create asynchronous collections of Promises and be able to use such methods as the map, filter, reduce and other Array#extras methods that you are used to using.

import * as Ix from 'ix';
 
// CommonJS 
const Ix = require('ix');
 
async function* gen() {
  yield 1;
  yield 2;
  yield 3;
  yield 4;
}
 
Ix.AsyncIterable.from(gen())
  .filter(x => x % 2 === 0)
  .map(x => x * 2)
  .forEach(x => console.log(`Next ${x}`))
  .catch(err => console.log(`Error ${err}`));
 
// => 4 
// => 8 

Much like with the Iterable object where we can iterate through our collections, we can use for await ... of instead which allows us to iterate over the asynchronous collection.

import * as Ix from 'ix';
 
// CommonJS 
const Ix = require('ix');
 
async function* gen() {
  yield 1;
  yield 2;
  yield 3;
  yield 4;
}
 
const results = Ix.AsyncIterable.from(gen())
  .filter(x => x % 2 === 0)
  .map(x => x * 2);
 
for await (let item of results) {
  console.log(`Next ${x}`);
}
 
// => 4 
// => 8 

Instead of bringing in the entire library for AsyncIterable, we can pick and choose which operators we want, for bundling concerns.

// ES 
import { AsyncIterableX as AsyncIterable } from 'ix/asynciterable';
import 'ix/add/asynciterable/of';
import 'ix/add/asynciterable-operators/map';
 
// CommonJS 
const AsyncIterable = require('ix/asynciterable').AsyncIterableX;
require('ix/add/asynciterable/of');
require('ix/add/asynciterable-operators/map');
 
const results = AsyncIterable.of(1,2,3)
  .map(x => x + '!!');

We can also bring in only the operators that we want to using just the operators themselves. Many of these operators take a simple AsyncIterable source from async function* functions such as the map and filter functions.

// ES 
import { map } from 'ix/asynciterable/map';
import { filter } from 'ix/asynciterable/filter';
 
// CommonJS 
const map = require('ix/asynciterable/map').map;
const filter = require('ix/asynciterable/filter').filter;
 
const source = async function* () {
  yield 1;
  yield 2;
  yield 3;
  yield 4;
};
 
const results = map(
  filter(
    source(), 
    x => x % 2 === 0
  ),
  x => x * x
);
 
for await (let item of results) {
  console.log(`Next: ${item}`);
}

Much like with the Iterable object, we can mix the two approaches for the AsyncIterable object by adding the minimal chain operator which then allows us to create a more fluent style but yet keeping the surface area to a minimum.

// ES 
import { AsyncIterableX as AsyncIterable } from 'ix/asynciterable';
import 'ix/add/asynciterable-operators/chain';
import { from } from 'ix/asynciterable/from';
import { filter } from 'ix/asynciterable/filter';
import { map } from 'ix/asynciterable/map';
 
// CommonJS 
const Iterable = require('ix/asynciterable').IterableX;
require('ix/add/asynciterable-operators/chain');
const from = require('ix/asynciterable/from');
const filter = require('ix/asynciterable/filter');
const map = require('ix/asynciterable/map');
 
 
const source = async function* () {
  yield 1;
  yield 2;
  yield 3;
  yield 4;
};
 
const results = from(source())
  .chain(source => filter(source, async x => x % 2 === 0))
  .chain(source => map(source, async x => x * x));
 
for await (let item of results) {
  console.log(`Next: ${item}`);
}

The AsyncIterable class implements the async iterator pattern in JavaScript by exposing the [Symbol.asyncIterator] method which in turn exposes the AsyncIterator class. The iterator yields values by calling the next() method which returns a Promise which resolves a IteratorResult class.

interface AsyncIterable<T> {
  [Symbol.asyncIterator](): AsyncIterator<T>;
}
 
interface AsyncIterator<T> {
  [Symbol.asyncIterator](): AsyncIterator<T>;
  next(value?: any): Promise<IteratorResult<T>>;
  return?(value?: any): Promise<IteratorResult<T>>;
  throw?(e?: any): Promise<IteratorResult<T>>;
}
 
interface IteratorResult<T> {
  value: T;
  done: Boolean;
}

Converting from Iterable to AsyncIterable

Using IxJS, you can easily go from an Iterable to an AsyncIterable using a number of methods. First, we can use the from function, either as a standalone or on the Ix.AsyncIterable object. The from method accepts a standard Iterable, Generator, and Iterator of Promises, or even another AsyncIterable.

import { from } from 'ix/asynciterable/from';
import { map } from 'ix/asynciterable/map';
 
const xs = [1, 2, 3, 4];
const asyncIterable = from(xs);
 
const mapped = map(asyncIterable, async (item, index) => item * index);
 
for await (let item of mapped) {
  console.log(`Next: ${item}`);
}

In addition, you can use the specialized async methods that are suffixed with Async, such as mapAsync, filterAsync, flatMapAsync amongst others. These functions accept async functions which allow you to return a Promise as the result.

import { mapAsync } from 'ix/iterable/mapasync';
 
const xs = [1, 2, 3, 4];
const mapped = mapAsync(xs, async (item, index) => item * index);
 
for await (let item of mapped) {
  console.log(`Next: ${item}`);
}

Contributing

We are grateful for contributions to the IxJS project. The IxJS project evolves because of community involvemnent from people such as yourselves. Please read below on how to get involved.

Code Of Conduct

The IxJS project has a strict Code of Conduct that must be adhered at all times. This code of conduct comes from the Contributor Convenant. Please read the full text as to what is and is not permitted.

Contributing Guide

Read the Contributing Guide on how to get involved with the IxJS project. This includes our development process and how to test your code before committing.

Packaging

IxJS is written in TypeScript, but the project is compiled to multiple JS versions and common module formats. The base IxJS package includes all the compilation targets for convenience, but if you're conscientious about your node_modules footprint, don't worry -- we got you. The targets are also published under the @reactivex namespace:

npm install @reactivex/ix-es5-cjs # ES5 CommonJS target  
npm install @reactivex/ix-es5-esm # ES5 ESModules target  
npm install @reactivex/ix-es5-umd # ES5 UMD target  
npm install @reactivex/ix-es5-cls # ES5 Google Closure Compiler target  
npm install @reactivex/ix-es2015-cjs # ES2015 CommonJS target  
npm install @reactivex/ix-es2015-esm # ES2015 ESModules target  
npm install @reactivex/ix-es2015-umd # ES2015 UMD target  
npm install @reactivex/ix-es2015-cls # ES2015 Google Closure Compiler target  
npm install @reactivex/ix-esnext-esm # ESNext CommonJS target  
npm install @reactivex/ix-esnext-esm # ESNext ESModules target  
npm install @reactivex/ix-esnext-umd # ESNext UMD target  
npm install @reactivex/ix-esnext-cls # ESNext Google Closure Compiler target  

Why do we package like this?

The JS community is a diverse group with a varied list of target environments and tool chains. Publishing multiple packages accommodates projects of all types. Friends targeting the latest JS runtimes can pull in the ESNext + ESM build. Friends needing wide browser support and small download size can use the UMD bundle, which has been run through Google's Closure Compiler with advanced optimizations.

If you think we missed a compilation target and it's a blocker for adoption, please open an issue. We're here for you ❤️.

License

The MIT License (MIT)

Copyright (c) ReactiveX

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.