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
54
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
74
Micro Frontends - A microservice approach to the modern web - O'Reilly Software Architecture Berlin 2019
ivanjov
0
64
React State - The Good, the Bad and the Ugly - ArmadaJS
ivanjov
0
100
Thinking Reactive in JavaScript - Sphere.it JS Krakow
ivanjov
0
60
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
150
Software engineer marketing done right – career tips from my experience.
ivanjov
0
34
Micro Frontends - A microservice approach to the modern web - Full Stack London 2018
ivanjov
0
220
Other Decks in Technology
See All in Technology
いま注目のAIエージェントを作ってみよう
supermarimobros
0
350
初めてAWSを使うときのセキュリティ覚書〜初心者支部編〜
cmusudakeisuke
1
280
2025/09/16 仕様駆動開発とAI-DLCが導くAI駆動開発の新フェーズ
masahiro_okamura
0
120
テストを軸にした生き残り術
kworkdev
PRO
0
210
OCI Oracle Database Services新機能アップデート(2025/06-2025/08)
oracle4engineer
PRO
0
180
普通のチームがスクラムを会得するたった一つの冴えたやり方 / the best way to scrum
okamototakuyasr2
0
110
AI時代を生き抜くエンジニアキャリアの築き方 (AI-Native 時代、エンジニアという道は 「最大の挑戦の場」となる) / Building an Engineering Career to Thrive in the Age of AI (In the AI-Native Era, the Path of Engineering Becomes the Ultimate Arena of Challenge)
jeongjaesoon
0
240
LLM時代のパフォーマンスチューニング:MongoDB運用で試したコンテキスト活用の工夫
ishikawa_pro
0
170
現場で効くClaude Code ─ 最新動向と企業導入
takaakikakei
1
260
Claude Code でアプリ開発をオートパイロットにするためのTips集 Zennの場合 / Claude Code Tips in Zenn
wadayusuke
5
840
Snowflake Intelligenceにはこうやって立ち向かう!クラシルが考えるAI Readyなデータ基盤と活用のためのDataOps
gappy50
0
280
AIエージェントで90秒の広告動画を制作!台本・音声・映像・編集をつなぐAWS最新アーキテクチャの実践
nasuvitz
3
340
Featured
See All Featured
Agile that works and the tools we love
rasmusluckow
330
21k
Become a Pro
speakerdeck
PRO
29
5.5k
"I'm Feeling Lucky" - Building Great Search Experiences for Today's Users (#IAC19)
danielanewman
229
22k
Visualization
eitanlees
148
16k
Bash Introduction
62gerente
615
210k
Save Time (by Creating Custom Rails Generators)
garrettdimon
PRO
32
1.6k
Typedesign – Prime Four
hannesfritz
42
2.8k
Understanding Cognitive Biases in Performance Measurement
bluesmoon
29
1.9k
The MySQL Ecosystem @ GitHub 2015
samlambert
251
13k
Learning to Love Humans: Emotional Interface Design
aarron
273
40k
Practical Orchestrator
shlominoach
190
11k
The Psychology of Web Performance [Beyond Tellerrand 2023]
tammyeverts
49
3k
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!