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)
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 ${item}`);
}
// => 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 filter = 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}`);
}
// Next 4
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').of;
const filter = require('ix/iterable/filter').filter;
const map = require('ix/iterable/map').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;
}
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}`));
// => Next 4
// => Next 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}`);
}
// => Next 4
// => Next 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;
}
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}`);
}
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.
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.
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.
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-ts # TypeScript target
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-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-esnext-esm # ESNext CommonJS target
npm install @reactivex/ix-esnext-esm # ESNext ESModules target
npm install @reactivex/ix-esnext-umd # ESNext UMD target
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 ❤️.
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.
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