You don't know Promises - IT Konekt April 2019

Transcript

1. You don't know Promises
2. I am Ivan Jovanovic Senior Software Engineer, Tech Speaker You can find me at @ivanjov96 or https://ivanjov.com Hello! IJ Consulting
3. Why I don't know Promises?
6. I am here today To show you how Promises really work!
7. 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
8. Only one thread And the event loop
10. How do we handle async code? Promises Callbacks Async/await
11. Callbacks Where everything began... 1
12. “ A callback is a function that is passed as an argument and will be executed after another function has finished executing.
15. Promises Changed everything 2
16. “ The Promise object represents the eventual completion (or failure) of an asynchronous operation, and its resulting value.
19. How Promises really work? The answer is a Microtask queue!
21. 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
23. Next TICK ONE Next TICK TWO TIMEOUT AFTER-ONE TIMEOUT AFTER-TWO
24. Promise methods ‒ Promise.all(iterable) ‒ Promise.race(iterable) ‒ Promise.resolve(value) ‒ Promise.reject(reason)
25. Promise.all(iterable)
26. Rejected situation
27. Promise.race(iterable)
28. Promisify non-Promise code
29. Native Promises from libraries
30. Async/await Comes to the rescue 3
31. “ Async/Await is a special syntax for working with Promises.
33. Most common problems with Promises that we see every day! 9
34. Nested promises 1
37. Broken Promise chain 2
40. Mixing sync and async code 3
44. Missing catch 4
48. Forget to return a Promise 5
51. Promisified synchronous code 6
53. Mixing Promise and Async/Await 7
56. Async function that returns Promise 8
60. Define a callback as an async function 9
62. Clinic.js https://clinicjs.org/
63. 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!
64. Any questions ? You can find me at ‒ @ivanjov96 ‒ hi@ivanjov.com Thanks!