Upgrade to Pro
— share decks privately, control downloads, hide ads and more …
Speaker Deck
Features
Speaker Deck
PRO
Sign in
Sign up for free
Search
Search
You don't know Promises - IT Konekt April 2019
Search
Ivan Jovanovic
April 20, 2019
Technology
1
47
You don't know Promises - IT Konekt April 2019
Ivan Jovanovic
April 20, 2019
Tweet
Share
More Decks by Ivan Jovanovic
See All by Ivan Jovanovic
Micro Frontends - A microservice approach to the modern web - Oredev 2019
ivanjov
0
69
Micro Frontends - A microservice approach to the modern web - O'Reilly Software Architecture Berlin 2019
ivanjov
0
57
React State - The Good, the Bad and the Ugly - ArmadaJS
ivanjov
0
89
Thinking Reactive in JavaScript - Sphere.it JS Krakow
ivanjov
0
48
Micro Frontends - A microservice approach to the modern web - PHPSrbija
ivanjov
0
200
Micro Frontends - A microservice approach to the modern web - Codemotion Rome 2019
ivanjov
0
320
Mikro Frontendi - Uvod - Novi Sad JS
ivanjov
0
130
Software engineer marketing done right – career tips from my experience.
ivanjov
0
27
Micro Frontends - A microservice approach to the modern web - Full Stack London 2018
ivanjov
0
170
Other Decks in Technology
See All in Technology
GraphRAGを用いたLLMによるパーソナライズド推薦の生成
naveed92
0
190
Amazon_CloudWatch_ログ異常検出_導入ガイド
tsujiba
4
1.8k
신뢰할 수 있는 AI 검색 엔진을 만들기 위한 Liner의 여정
huffon
0
530
フルカイテン株式会社 採用資料
fullkaiten
0
39k
[JAWS-UG金沢支部×コンテナ支部合同企画]コンテナとは何か
furuton
3
330
2024年グライダー曲技世界選手権参加報告/2024 WGAC report
jscseminar
0
140
"君は見ているが観察していない"で考えるインシデントマネジメント
grimoh
4
960
Microsoft Intune アプリのトラブルシューティング
sophiakunii
1
370
軽量DDDはもういらない! スタイルガイド本で OOPの実装パターンを学ぼう
panda_program
29
11k
Engineering at LY Corporation
lycorp_recruit_jp
0
160
データ活用促進のためのデータ分析基盤の進化
takumakouno
2
120
What to do after `laravel new`
mattstauffer
0
130
Featured
See All Featured
Learning to Love Humans: Emotional Interface Design
aarron
273
40k
Statistics for Hackers
jakevdp
796
220k
Reflections from 52 weeks, 52 projects
jeffersonlam
346
20k
The Cult of Friendly URLs
andyhume
78
6k
GraphQLの誤解/rethinking-graphql
sonatard
67
10k
Put a Button on it: Removing Barriers to Going Fast.
kastner
59
3.5k
Practical Tips for Bootstrapping Information Extraction Pipelines
honnibal
PRO
10
700
Understanding Cognitive Biases in Performance Measurement
bluesmoon
26
1.4k
Unsuck your backbone
ammeep
668
57k
Code Reviewing Like a Champion
maltzj
520
39k
The Psychology of Web Performance [Beyond Tellerrand 2023]
tammyeverts
42
2.2k
Cheating the UX When There Is Nothing More to Optimize - PixelPioneers
stephaniewalter
280
13k
Transcript
You don't know Promises
I am Ivan Jovanovic Senior Software Engineer, Tech Speaker You
can find me at @ivanjov96 or https://ivanjov.com Hello! IJ Consulting
Why I don't know Promises?
None
None
I am here today To show you how Promises really
work!
JavaScript is strange because ‒ It was built for 10
days ‒ It has one thread ‒ It is synchronous and asynchronous ‒ It is everywhere ‒ It is different
Only one thread And the event loop
None
How do we handle async code? Promises Callbacks Async/await
Callbacks Where everything began... 1
“ A callback is a function that is passed as
an argument and will be executed after another function has finished executing.
None
None
Promises Changed everything 2
“ The Promise object represents the eventual completion (or failure)
of an asynchronous operation, and its resulting value.
None
None
How Promises really work? The answer is a Microtask queue!
None
Microtask queue ‒ Independent queue ‒ Used by: process.nextTick, Promises,
Object.observe, MutationObserver ‒ Faster than the main queue and may be drained several times in a single event loop tick
None
Next TICK ONE Next TICK TWO TIMEOUT AFTER-ONE TIMEOUT AFTER-TWO
Promise methods ‒ Promise.all(iterable) ‒ Promise.race(iterable) ‒ Promise.resolve(value) ‒ Promise.reject(reason)
Promise.all(iterable)
Rejected situation
Promise.race(iterable)
Promisify non-Promise code
Native Promises from libraries
Async/await Comes to the rescue 3
“ Async/Await is a special syntax for working with Promises.
None
Most common problems with Promises that we see every day!
9
Nested promises 1
None
None
Broken Promise chain 2
None
None
Mixing sync and async code 3
None
None
None
Missing catch 4
None
None
None
Forget to return a Promise 5
None
None
Promisified synchronous code 6
None
Mixing Promise and Async/Await 7
None
None
Async function that returns Promise 8
None
None
None
Define a callback as an async function 9
None
Clinic.js https://clinicjs.org/
Conclusion ‒ JS is crazy and great at the same
time! ‒ Async behavior is a pro, not a con. ‒ Be careful when using Promises, it's great and dangerous at the same time!
Any questions ? You can find me at ‒ @ivanjov96
‒
[email protected]
Thanks!