5 Architectures of
Asynchronous JavaScript

Tomasz Ducin

@tomasz_ducin

5 Architectures of Asynchronous JavaScript

Tomasz Ducin

7th June 2019, Amsterdam

5 Architectures of Asynchronous JavaScript

5 Architectures of Asynchronous JavaScript

Tomasz Ducin

11th October 2017, Warsaw

#38

Tomasz Ducin

10th October 2017, Warsaw

#216

5 Architectures of Asynchronous JavaScript

5 Architectures of Asynchronous JavaScript

5 Architectures of Asynchronous JavaScript

Tomasz Ducin

Tomasz Ducin

Tomasz Ducin

13th July 2017, London

FullStack

FullStack

5 Architectures of Asynchronous JavaScript

conference on JavaScript, Node & Internet of Things

conference on JavaScript, Node & Internet of Things

Tomasz Ducin

13th July 2017, London

5 Architectures of Asynchronous JavaScript

Tomasz Ducin

22nd June 2017, Kraków

5 Architectures of
Asynchronous JavaScript

Tomasz Ducin

3rd April 2017, Warsaw

5 Architectures of
Asynchronous JavaScript

Tomasz Ducin

30th March 2017, Warsaw

5 Architectures of
Asynchronous JavaScript

Tomasz Ducin

developer & architect

independent consultant

trainer @ Bottega IT Minds

@tomasz_ducin

ducin

ducin.it

functions

sync vs async

promises

async await

coroutines

CSP

generators

callbacks

events

reactive streams

run to completion

event loop

sync vs async

blocking vs non-blocking

code is linear; execution:

linear vs non-linear

learn by metaphors

Concurrent

Parallel

no thread synchronization

no deadlocks

Concurrency

cooperative

vs

preemptive

setInterval & setTimeout

UX/performance issues

function-first

  • scopes

  • closures

  • context, binding

  • legacy (hoisting, IIFEs)

  • FP, side effects, purity

  • etc.

list.forEach(function(item){
  ...
});

synchronous

asynchronous

setTimeout(function(){
  ...
}, delay);
var list = [1,2,3];
console.log("before");
list.forEach(function(item){
  console.log(item);
});
console.log("after");
console.log("before");
setTimeout(function(){
  console.log("inside");
}, 0);
console.log("after");

callbacks

asynchronous

setTimeout(function(){
  ...
}, delay);
......................
...........function(){
  console.log("inside");
}.....
.....................

callbacks

event loop

message queue

one thing at a time

(single thread) 

(function() {
    console.log(1); 
    setTimeout(function(){console.log(2)}, 1000); 
    setTimeout(function(){console.log(3)}, 0); 
    console.log(4);
})();
console.log(5);

run to completion

(function() {
    console.log(1); 
    setTimeout(.........................., 1000); 
    setTimeout(.........................., 0); 
    console.log(4);
})();
console.log(5);
.............
    ............... 
    ............................................. 
    ...........function(){console.log(3)}..... 
    ............... 
.....
...............
.............
    ............... 
    ...........function(){console.log(2)}........ 
    .......................................... 
    ............... 
.....
...............

Registering callbacks

$(document).ready(function() {
  $('.pull-me').click(function() {
    $('.panel').slideToggle('slow');
  });
});

& run to completion

var customers;

// usually takes 0,5s
ajax.get('customers', {
  success: function(data){
    customers = data;
  }
});

assumptions about
async order 

var customers, products;

// usually takes 0,5s
ajax.get('customers', {
  success: function(data){
    customers = data;
  }
});

// usually takes 2s
ajax.get('products', {
  success: function(data){
    doSomething(customers, data);
  }
});
connection.query('CREATE DATABASE IF NOT EXISTS test', function (err) {
    if (err) throw err;
    connection.query('USE test', function (err) {
        if (err) throw err;
        connection.query('CREATE TABLE IF NOT EXISTS users('
            + 'id INT NOT NULL AUTO_INCREMENT,'
            + 'PRIMARY KEY(id),'
            + 'name VARCHAR(30)'
            +  ')', function (err) {

            });
    });
});
connection.query('CREATE DATABASE IF NOT EXISTS test', function (err) {











});
connection.query('CREATE DATABASE IF NOT EXISTS test', function (err) {
    if (err) throw err;
    connection.query('USE test', function (err) {








    });
});
connection.query('CREATE DATABASE IF NOT EXISTS test', function (err) {
    if (err) throw err;
    connection.query('USE test', function (err) {
        if (err) throw err;
        connection.query('CREATE TABLE IF NOT EXISTS users('
            + 'id INT NOT NULL AUTO_INCREMENT,'
            + 'PRIMARY KEY(id),'
            + 'name VARCHAR(30)'
            +  ')', function (err) {
                if (err) throw err;
            });
    });
});

callback hell

flying V

pyramid of doom

fs.readdir(source, function (err, files) {
  if (err) {
    console.log('Error finding files: ' + err)
  } else {
    files.forEach(function (filename, fileIndex) {
      console.log(filename)
      gm(source + filename).size(function (err, values) {
        if (err) {
          console.log('Error identifying file size: ' + err)
        } else {
          console.log(filename + ' : ' + values)
          aspect = (values.width / values.height)
          widths.forEach(function (width, widthIndex) {
            height = Math.round(width / aspect)
            console.log('resizing ' + filename + 'to ' + height + 'x' + height)
            this.resize(width, height).write(dest + 'w' + width + '_' + filename, function(err) {
              if (err) console.log('Error writing file: ' + err)
            })
          }.bind(this))
        }
      })
    })
  }
})

Callback hell

a Promise of
a single operation
to be completed in future 

fetchData()
.then(callbackFn)
.catch(errorHandlerFn)
myCustomOperation()
.then(callbackFn)
.catch(errorHandlerFn)

Promise - states

pending

fulfilled

rejected

initial state,
not settled yet

operation has failed

operation has completed successfully

settled

promise limitations

  • single item

  • one-time item

  • greedy

  • not cancellable

  • values unavailable outside the chain

  • only previous step value available 


  return asyncOp1();
function promiseChain(){
  return asyncOp1()
    .then(asyncOp2)
    .then(asyncOp3)
    .then(asyncOp4);
}

  return asyncOp1()
    .then(asyncOp2);

  return asyncOp1()
    .then(asyncOp2)
    .then(asyncOp3);

  return asyncOp1()
    .then(asyncOp2)
    .then(asyncOp3)
    .then(asyncOp4);

function sequential(){
  return asyncOp1()
    .then(asyncOp2)
    .then(asyncOp3)
    .then(asyncOp4);
}

Sequential Processing

op1
op2
op3
op4
sequential()
  .then(anotherAsync)
another
function parallel(){
  var p1 = asyncOp1();
  var p2 = asyncOp2();
  var p3 = asyncOp3();
  var p4 = asyncOp4();
  return Promise.all(
    [p1, p2, p3, p4]);
}

Concurrent Processing

op1
another
.all
parallel()
  .then(anotherAsync)
op2
op3
op4
Promise.all([p1, p2, p3, p4])
  .then( ([v1, v2, v3, v4]) => {...})
  .catch( reason => {...})

Promise Aggregates

Promise.race([p1, p2, p3, p4])
  .then( value => {...})
  .catch( reason => {...})
Promise.any([p1, p2, p3, p4])
  .then( value => {...})
  .catch( ([r1, r2, r3, r4]) => {...})

all
race
any
Promise.some([p1, p2, p3, p4], 2)
  .then( (v1, v2) => {...})
  .catch( ([r1, r2, r3]) => {...})

some
function zeroOneTwo(){
  return [0, 1, 2];
}
function* zeroOneTwo(){
  yield 0;
  yield 1;
  yield 2;
}

lazy

greedy

list

generator

synchronous

synchronous

for (var i of zeroOneTwo()) {
  console.log(i);
} // 1 2 3
function* generator(){
  console.log(1, "inside");
  yield "A";
  console.log(2, "inside");
  yield "B";
}

var iterator = generator();
console.log(1, "outside");
iterator.next();
console.log(2, "outside");
iterator.next();
console.log(3, "outside");

synchronous

Generators

vs run to completion

1: outside
1: inside
2: outside
2: inside
3: outside
function* generate(){
  console.log(1, "inside");
  let recv = yield "A";
  console.log(2, "inside", recv);
  yield "B";
}

var iter = generate();
console.log(1, "outside");
let item = iter.next();
console.log(2, "outside", item.value);
iter.next('hey!');
console.log(3, "outside");

synchronous

Generators

vs run to completion

1: outside
1: inside
2: outside, A
2: inside, hey!
3: outside

= coroutines

promises + generators

+ 1 tiny wrapper

  • start immediately
  • suspend on promise
     
  • resume when settled
  • promise pending...
  • resolve/ reject calls next

writing asynchronous code in synchronous manner 

function* sequential(){
  var v1 = yield asyncOp1();
  var v2 = yield asyncOp2(v1);
  var v3 = yield asyncOp3(v2);
  return asyncOp4(v3);
}
let asyncSequential
  = async(sequential);

Sequential Processing

asyncSequential()
  .then(anotherAsync)
op1
op2
op3
op4
another
function* parallel(){
  var p1 = asyncOp1();
  var p2 = asyncOp2();
  var p3 = asyncOp3();
  var p4 = asyncOp4();
  return yield p1 + yield p2
    + yield p3 + yield p4;
}
let asyncParallel
  = async(parallel)
asyncParallel()
  .then(anotherAsync)
op1
another
.all
op2
op3
op4

Concurrent Processing

function async(makeGenerator){
  return function () {
    var generator = makeGenerator.apply(this, arguments);

    function handle(result){
      // result => { done: [Boolean], value: [Object] }
      if (result.done) return Promise.resolve(result.value);
      return Promise.resolve(result.value).then(function (res){
        return handle(generator.next(res));
      }, function (err){
        return handle(generator.throw(err));
      });
    }

    try {
      return handle(generator.next());
    } catch (ex) {
      return Promise.reject(ex);
    }
  }
}

a couple of lines that
do the right thing...

ES2017 / ES8

async function sequential(){
  var v1 = await asyncOp1();
  var v2 = await asyncOp2(v1);
  var v3 = await asyncOp3(v2);
  return asyncOp4(v3);
}

Sequential Processing

sequential()
  .then(anotherAsync)
op1
op2
op3
op4
another
async function parallel(){
  var p1 = asyncOp1();
  var p2 = asyncOp2();
  var p3 = asyncOp3();
  var p4 = asyncOp4();
  return await p1 + await p2
    + await p3 + await p4;
}
parallel()
  .then(anotherAsync)
op1
another
.all
op2
op3
op4

Concurrent Processing

async/await usecase 

model {
  beginTransfer(): Promise<TransferID> {
    return HTTP.post('/transfers');
  }











}
model {
  beginTransfer(): Promise<TransferID> {
    return HTTP.post('/transfers');
  }

  setTransferDetails(
    transferID: TransferID,
    details: TransferDetails
  ): Promise<void> {
    return HTTP.post(`/transfers/${transferID}`, details);
  }




}
model {
  beginTransfer(): Promise<TransferID> {
    return HTTP.post('/transfers');
  }

  setTransferDetails(
    transferID: TransferID,
    details: TransferDetails
  ): Promise<void> {
    return HTTP.post(`/transfers/${transferID}`, details);
  }

  confirmTransfer(transferID: TransferID): Promise<?> {
    return HTTP.post(`/transfers/${transferID}`, {action: "confirm"});
  }
}
model {














}
async function scheduleTransfer(component){
  let transferID = await model.beginTransfer();









}
async function scheduleTransfer(component){
  let transferID = await model.beginTransfer();
  // waiting for user to input data
  await component.completedStep1();
  await model.setTransferDetails(transferID, details);
  // waiting for user confirmation
  await component.completedStep2();
  await model.confirmTransfer(transferID);
  // waiting for user closing popup
  await component.completedStep3();
  return transferID;
}

async function scheduleTransfer(component){
  let transferID = await model.beginTransfer();
  // waiting for user to input data
  await component.completedStep1();







}

async function scheduleTransfer(component){
  let transferID = await model.beginTransfer();
  // waiting for user to input data
  await component.completedStep1();
  await model.setTransferDetails(transferID, details);






}

async function scheduleTransfer(component){
  let transferID = await model.beginTransfer();
  // waiting for user to input data
  await component.completedStep1();
  await model.setTransferDetails(transferID, details);
  // waiting for user confirmation
  await component.completedStep2();




}
async function scheduleTransfer(component){
  let transferID = await model.beginTransfer();
  // waiting for user to input data
  await component.completedStep1();
  await model.setTransferDetails(transferID, details);
  // waiting for user confirmation
  await component.completedStep2();
  await model.confirmTransfer(transferID);



}

async function scheduleTransfer(component){
  let transferID = await model.beginTransfer();
  // waiting for user to input data
  await component.completedStep1();
  await model.setTransferDetails(transferID, details);
  // waiting for user confirmation
  await component.completedStep2();
  await model.confirmTransfer(transferID);
  // waiting for user closing popup
  await component.completedStep3();

}

function scheduleTransfer(component){
  return model.beginTransfer()
  .then(transferID => {
    // waiting for user to input data
    return component.completedStep1()
    .then(() => model.setTransferDetails(transferID, details))
    // waiting for user confirmation
    .then(() => component.completedStep2())
    .then(() => model.confirmTransfer(transferID))
    .then(() => component.completedStep3())
    .then(() => transferID);
  })
}
  • many nested function calls
  • callback hell again

Pipeline scope

function promiseChain(){
  return asyncOp1()
    .then(asyncOp2)
    .then(asyncOp3)
    .then(asyncOp4 ???);
}

using data from previous steps

async function sequential(){
  var v1 = await asyncOp1();
  var v2 = await asyncOp2(v1);
  var v3 = await asyncOp3(v2);
  return asyncOp4(v1, v2, v3);
}

No nested functions

same as in generators

async function renderChapters(urls) {
  urls.map(getJSON)
    .forEach(p => addToPage((await p).html));
}
async function renderChapters(urls) {
  urls.map(getJSON)
    .forEach(async p => addToPage((await p).html));
}
                                Syntax Error
                            
                                parallel

Async Arrow Functions

(async x => x ** 2);
(async x => { return x ** 2; });
(async (x, y) => x ** y);
(async (x, y) => { return x ** y; });

instead of Promise.resolve

const square = (async x => x ** 2);
square(5) // same as Promise.resolve(25)

square(5).then(console.log)
// output: 25

Async Iteration

stage 3 proposal 

for await (const line of readLines(filePath)) {
  console.log(line);
}
syncIterator.next()
// -> { value: ..., done: ... }
asyncIterator.next()
// -> Promise resolving with
//    { value: ..., done: ... }
.then(({ value, done }) => /* ... */);

lazy and asynchronous

Top-level await

// all awaited functions return a promise
// all awaited functions return a promise

await delay(2000);
// all awaited functions return a promise

await delay(2000);

// webservices
const flowers = await fetch('flowers.jpg');
// all awaited functions return a promise

await delay(2000);

// webservices
const flowers = await fetch('flowers.jpg');

// I/O operations
let content = '...';
let fileName = 'filename.json';
await writeFile(fileName, content);
await doSomeProcessing(fileName);

Top-level await is a footgun

Rich Harris, creator of Rollup

var data = await something();
// import gets blocked
import { m } from 'module';

m.run();
if (!Array.prototype.myMethod){
  ...
  await something();
}
var data = await something();
export default data;

module.js

Top-level await

consumer.js

Communicating Sequential Processes

C
S
P 

import {go, chan, take, put} from 'js-csp';

let chA = chan();
let chB = chan();
js-csp
yield put
yield take
chan
go
csp.go(function* () {
  const rec1 = yield csp.take(chA);
  console.log('A > RECEIVED:', rec1);

  const sent2 = 'cat';
  console.log('A > SENDING:', sent2);
  yield csp.put(chB, sent2);

  const rec3 = yield csp.take(chA);
  console.log('A > RECEIVED:', rec3);
});
csp.go(function* () {
  const sent1 = 'dog';
  console.log('B > SENDING:', sent1);
  yield csp.put(chA, sent1);

  const rec2 = yield csp.take(chB);
  console.log('B > RECEIVED:', rec2);

  const sent3 = 'WAT!';
  console.log('B > SENDING:', sent3);
  yield csp.put(chA, sent3);
});
=> B > SENDING: dog
=> A > RECEIVED: dog
=> A > SENDING: cat
=> B > RECEIVED: cat
=> B > SENDING: WAT!
=> A > RECEIVED: WAT!

process B

process A

csp.go(function* () {









});
csp.go(function* () {










});

process B

process A

csp.go(function* () {
  const rec1 = yield csp.take(chA);








});
csp.go(function* () {
  const sent1 = 'dog';
  console.log('B > SENDING:', sent1);








});
=> B > SENDING: dog
=> B > SENDING: dog
=> A > RECEIVED: dog
csp.go(function* () {
  const rec1 = yield csp.take(chA);
  console.log('A > RECEIVED:', rec1);







});
csp.go(function* () {
  const rec1 = yield csp.take(chA);
  console.log('A > RECEIVED:', rec1);

  const sent2 = 'cat';
  console.log('A > SENDING:', sent2);




});
csp.go(function* () {
  const sent1 = 'dog';
  console.log('B > SENDING:', sent1);
  yield csp.put(chA, sent1);

  const rec2 = yield csp.take(chB);





});
=> B > SENDING: dog
=> A > RECEIVED: dog
=> A > SENDING: cat
csp.go(function* () {
  const rec1 = yield csp.take(chA);
  console.log('A > RECEIVED:', rec1);

  const sent2 = 'cat';
  console.log('A > SENDING:', sent2);
  yield csp.put(chB, sent2);

  const rec3 = yield csp.take(chA);

});
csp.go(function* () {
  const sent1 = 'dog';
  console.log('B > SENDING:', sent1);
  yield csp.put(chA, sent1);

  const rec2 = yield csp.take(chB);
  console.log('B > RECEIVED:', rec2);




});
=> B > SENDING: dog
=> A > RECEIVED: dog
=> A > SENDING: cat
=> B > RECEIVED: cat
csp.go(function* () {
  const sent1 = 'dog';
  console.log('B > SENDING:', sent1);
  yield csp.put(chA, sent1);

  const rec2 = yield csp.take(chB);
  console.log('B > RECEIVED:', rec2);

  const sent3 = 'WAT!';
  console.log('B > SENDING:', sent3);

});
=> B > SENDING: dog
=> A > RECEIVED: dog
=> A > SENDING: cat
=> B > RECEIVED: cat
=> B > SENDING: WAT!
csp.go(function* () {
  const sent1 = 'dog';
  console.log('B > SENDING:', sent1);
  yield csp.put(chA, sent1);

  const rec2 = yield csp.take(chB);
  console.log('B > RECEIVED:', rec2);

  const sent3 = 'WAT!';
  console.log('B > SENDING:', sent3);
  yield csp.put(chA, sent3);
});
csp.go(function* () {
  const rec1 = yield csp.take(chA);
  console.log('A > RECEIVED:', rec1);

  const sent2 = 'cat';
  console.log('A > SENDING:', sent2);
  yield csp.put(chB, sent2);

  const rec3 = yield csp.take(chA);
  console.log('A > RECEIVED:', rec3);
});
=> B > SENDING: dog
=> A > RECEIVED: dog
=> A > SENDING: cat
=> B > RECEIVED: cat
=> B > SENDING: WAT!
=> A > RECEIVED: WAT!

events

browser events

  • click
  • focus
  • mouse*
  • change
  • etc.

custom events

$(selector).on(event, function(e){
  // use `this` and `e`
});
$someone.on('click', function(){
  $element.trigger('custom');
});

$element.on('custom', function(){
  // logic
});
Backbone.on(event, this.render);
initialize: function() {
  this.listenTo(this.model,
    'change', this.render);
}

RxCpp

Rx.rb

RxPHP

RxJS

RxJava

RxPY

RxKotlin

RxSwift

RxLua

RxClojure

Rx.NET

UniRx

RxScala

RxGroovy

RxGo

RxDart

Array

Stream

[   ,   ,   ,   ,   ]

A

B

C

D

E

,

A

B

C

D

E

,

,

,

entirely in-memory

items pushed over time

completed

[1, 2, 3].map(e => e * 2)
         .map(e => e * 2)
stream$.map(e => e * 2)
  • all available upfront
  • in-memory
  • not necessarily exist
  • sync or async, doesn't matter
  • don't know when they arrive
  • push instead of pull
.subscribe(
  value => console.log(`value: ${value}`),
  ...
);
  • manipulating data
map, filter, find, reduce, sort...

Reactive Streams

  • manipulating data
  • manipulating time
    (when to become available)

Functors/HOF

Arrays

items go down the stream

rx marbles

The Hollywood Principle

const click$ = Rx.Observable.fromEvent(document, 'click');
const click$ = Rx.Observable.fromEvent(document, 'click')
.map(e => ({
  x: e.clientX,
  y: e.clientY
}))
.filter(e => e.x < document.body.clientWidth/2);
click$.subscribe(
  value => console.log(`value: ${value}`),
  e => console.warn(`error: ${e}`),
  () => console.log('completed')
);

observer

+ iterator

+ FP

1. data source

2. processing items

3. observers

Observable streams

are difficult

  • sync or async

  • one or many values

  • still opened or already closed

  • IoC (Holywood principle)

  • observer + iterator + FP

  • observables

  • observables, observers and subscriptions

  • when is the source created: hot and cold observables

  • re-emit: subjects

  • backpressure (lossy, loss-less)

is your app supposed to solve above issues?

demo time

HTTP calls as streams...?

getItems(onNext, onError) {
  this.http
    .get("/items")
    .map(response => response.json())
    .retry(2)
    .subscribe(onNext, onError)
}
@Component({
  selector: 'async-component',
  template: `<code>promise|async</code>
             <code>stream|async</code>`
})
export class AsyncComponent {
  private promise: Promise<any>;
  private stream: Observable<any>;

  constructor(){
    this.promise = new Promise((res, rej) => {
      setTimeout(() => res('item-p'), 1000)
    });

    this.stream = Observable.of('item-s')
      .delay(1000)
  }
}

async pipe 

promise.then(onSuccess, onFailure)
promise.catch(onFailure)
observable$
  .subscribe(onNext, onError, onCompleted)

promise API

observable API

async function process(args){
  let user = await API.getUser(args);
  let address = await API.getAddress(user);
  return { user, address };
}

async await API

functions

sync vs async

promises

async await

coroutines

CSP

generators

callbacks

events

reactive streams

run to completion

event loop

THX!

@tomasz_ducin

tomasz@ducin.it

bit.ly/5-async-js

5 Architectures of Asynchronous JavaScript

By Tomasz Ducin

5 Architectures of Asynchronous JavaScript

Abstract: In this talk we'll discuss 5 alternative approaches to handle async operations: callbacks, events, promises, coroutines and reactive streams. None of them is either legacy or a silver bullet - a good dev needs to pick the right tool for the job. However, in order to understand them, we must step back to fundamentals all these rely on: the mechanics of event loop and run to completion rule, as well as learn to distinguish between sync and async flow. Then we proceed to design patterns built on top of each of the 5 approaches, discussing their strengths and limitations. Funfacts, such as famous Promise.race() included!

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