JS: Async & Performance

Discussion of Promise pattern for JavaScript and your advantages front at normal callbacks use. Introduced the concept of WebWorkers and how it works.

Transcript

1. JavaScript Async & Performance
2. Now & Later concept Promises Program Performance
3. Now & Later concept
4. • Later doesn't happen necessary immediately after now • Javascript program composed by chunks of code
5. • What is the order of execution?
6. • JS engine itself execute a single chunk at any given moment, when asked to. • JS engine runs inside a hosting environment • It's the surrounding environment that has always scheduled events on event loop
7. Event Loop
8. Promises
9. • It normalizes the now and later • Behaves as a future value • On finish a task we can decide what to do next • Flow-control mechanism (this-then-that)
10. Promise example:
11. Separate parts of the code can be given the event listening capability
12. Other way
13. Advantages over Callback
14. • Call the callback too early • Even if that Promise was already resolved, the callback you provide to then(..) will always be called asynchronously
15. • Call the callback too late
16. • Promise Scheduling Quirks
17. • Never Calling the Callback
18. • Calling Too Few or Too Many Times • Promises are defined so that they can only be resolved once
19. • Swallowing Any Errors/Exceptions
20. Program Performance
21. • Parallel execution • Web worker (browser feature) • Multiple instances os JS engine each one in a thread. • Total independent processing • Not share scope or resources • Communication by event messages
23. • Data transfer between workers • Structured Cloning Algorithm • Transferable Objects
24. • Shared Workers • Dedicated worker for multiple tabs of same page • Communication by event messages by port
25. • You Don't Know JS: Async & Performance (https://github.com/getify/You-Dont-Know-JS/tree/master/async %20%26%20performance) Bibliography