A library of async iterator extensions for JavaScript including ```map```, ```reduce```, ```filter```, ```flatMap```, ```pipe``` and [more](https://github.com/jamiemccrindle/axax/blob/master/docs/API.md#functions).
npm install axaxA library of async iterator extensions for JavaScript including ``map`, `reduce`,`filter`, `flatMap`, `pipe` and more.
`bash`
npm install axax # or yarn add axax
Async iterators are a useful way to handle asynchronous streams. This library adds a number
of utility methods similar to those found in lodash, underscore, Ramda or RxJs.
Axax contains both transpiled es5 code as well as esnext code, the difference being that
esnext uses the native `for await` syntax. In nodejs 10.x that gives approximately a 40% speedup.
`javascript
// use es5 if you want to support more browsers
import { map } from "axax/es5/map";
// use esnext if you're only using node 10.x or supporting very new browsers
import { map } from "axax/esnext/map";
`
`fromEvent` turns DOM events into an iterable.
`javascript
import { fromEvent } from "axax/es5/fromEvent";
const clicks = fromEvent(document, 'click');
for await (const click of clicks) {
console.log('a button was clicked');
}
`
`fromLineReader` turns a NodeJS LineReader into an async iterable.
The example below prints the lines from a file in upper case after
filtering out the empty ones.
`javascript
// create the line reading async iterable
const lines = fromLineReader(
require("readline").createInterface({
input: require("fs").createReadStream("./data/example.txt")
})
);
// create a filter that removes empty lines
const notEmpty = filter(line => line.length > 0);
// convert to uppercase
const toUpperCase = map(line => line.toUpperCase());
// go through each of the non empty lines
for await (const line of pipe(notEmpty, toUpperCase)(lines)) {
console.log(line);
}
`
`Subject` makes it easy to turn stream of events into an iterable. The code below`
is essentially how fromEvent` was implemented.
`javascript
import { Subject } from "axax/es5/subject";
const subject = new Subject();
// set up a callback that calls value on the subject
const callback = value => subject.onNext(value);
// attach the callback to the click event
document.addEventListener('click', callback);
// remove the callback when / if the iterable stops
subject.finally(() => document.removeEventListener('click', callback));
// go through all the click events
for await (const click of subject.iterator) {
console.log('a button was clicked');
}
`
It's possible to have an async iterator leak if it never returns a value e.g.:
`javascript
const subject1 = new Subject();
const subject2 = new Subject();
async function* neverEnds() {
try {
for await(const i of subject2.iterator) {
yield i;
}
} finally {
console.log("never called")
}
}
async function* run() {
for await(const i of merge(subject1.iterator,neverEnds())) {
break;
}
}
run()
subject1.onNext(1)
``
If you need to be able to cancel async iterators that may never return values,
consider Rx or regular Observables for now.
(Thanks to @awto for the example)