Asynchronous Javascript

Async in JS

PLAN

Promises

Promise magic

Async/Await

Events & Callbacks

Promise overview

.then(), .catch(), parallel execution

Write async

ASYNC IN JS

EVENTS

The most basic form of asynchronous programming in JavaScript.

CALLBACKS: BASIC

Functions that are called after an asynchronous operation
Usually are passed

CALLBACKS: HARD

CALLBACKS: HELL

PROMISES

PROMISES

Operation that will return its result some time later
Multiple handlers of

.THEN

PROMISES & THENABLES

Promises are objects whose behaviour conforms to the Promise

CONSTRUCTOR

The function passed to new Promise() is called the executor.
.then ()

PROMISE STATES

A Promise is in one of three states:
pending: initial state,

WORKING WITH PROMISES

.THEN() MAGIC

.then() always returns a new promise
This new promise is resolved

.THEN() & NEW PROMISE

If you return a promise with .then (),

ERROR HANDLING

Promises can be rejected with reason
As a second argument, the

RECOVERY

Promises are able to "recover"
If you return a value from the

FAIL SILENTLY

If an error occurs in a promise that does not

CREATING COMPLETED PROMISES

Promise.resolve () and Promise.reject () allow you to create

BACK TO THENABLES

Promise.resolve () and Promise.reject () can take thenable arguments
They

PARALLEL EXECUTION: ALL

Promise.all() is waits for all promises to complete
Returns a

PARALLEL EXECUTION: RACE

Promise.race () creates a race among promises
Returns a new

ASYNC/AWAIT

ASYNC/AWAIT

ES7 introduced a new way to add async behaviour in JavaScript
Working

SUSPEND EXECUTION

await keyword suspends the asynchronous function and waits for the awaited value return

ADD SUGAR

Async/Await is just syntactic sugar for promises, so you can

ERROR HANDLING

Async/await allow us to handle errors the same way we