Streams, events and promises (node.js)

Jozi Node.js user group presentation

Transcript

1. JOZI.NODE.JS STREAMS, EVENTS AND PROMISES Created by /
2. NODE.JS ? Platform built on the V8 javascript engine Tyrannically asynchronous, devilishly event-oriented and amazoidingly non-blocking
3. ON THE RIGHT HAND SIDE / / s y n c c o d e - u n u s u a l v a r x = d o _ t h i s ( w i t h _ t h i s ) / / a s y n c - m o r e n a t u r a l d o _ s o m e t h i n g ( w i t h _ t h i s , c a l l _ m e _ w h e n _ d o n e ) ;
4. EVENTS ARE THE WAY events.EventEmitter s e r v e r . o n ( ' c o n n e c t i o n ' , f u n c t i o n ( s t r e a m ) { c o n s o l e . l o g ( ' s o m e o n e c o n n e c t e d ! ' ) ; } ) ; same as emitter.addListener(event, listener)
5. WHEN YOU ARE READY f u n c t i o n c o o k i n g C o m p l e t e d ( ) { e m i t t e r . e m i t ( ' c o o k e d ' , ' c h i c k e n ' } ) ; } e m i t t e r . o n ( ' c o o k e d ' , f u n c t i o n ( f o o d ) { c o n s o l e . l o g ( ' y o u r ' + f o o d + ' i s r e a d y ! ' ) ; } ) ;
6. EVENT DRIVEN ? Only a single thread, ever, seriously ! f o r ( v a r i = 1 ; i < = 3 ; i + + ) { s e t T i m e o u t ( f u n c t i o n ( ) { c o n s o l e . l o g ( i ) ; } , 0 ) ; } ;
7. EVENTS FTW ! v a r s t a r t = n e w D a t e ; s e t T i m e o u t ( f u n c t i o n ( ) { v a r e n d = n e w D a t e ; c o n s o l e . l o g ( ' T i m e e l a p s e d : ' , e n d - s t a r t , ' m s ' ) ; } , 5 0 0 ) ; w h i l e ( n e w D a t e - s t a r t < 1 0 0 0 ) { } ;
8. NO MORE INTERRUPTIONS ! You don't have to worry about your code being swapped out. No more stress about concurrency.
9. WTF ? No more stress about concurrency.
10. STREAMS Streams are an API for event sources and sinks. Streams all inherit from EventEmitter. Readable Writable Duplex Transform PassThrough
11. WHY ? so that we can pipe() things ! s r c . p i p e ( d s t )
12. READABLE STREAM so that we can pipe() things ! v a r R e a d a b l e = r e q u i r e ( ' s t r e a m ' ) . R e a d a b l e ; v a r r s = n e w R e a d a b l e ; r s . p u s h ( ' b e e p ' ) ; r s . p u s h ( ' b o o p \ n ' ) ; r s . p u s h ( n u l l ) ; r s . p i p e ( p r o c e s s . s t d o u t ) ;
13. LAZILY EFFICIENT v a r R e a d a b l e = r e q u i r e ( ' s t r e a m ' ) . R e a d a b l e ; v a r r s = R e a d a b l e ( ) ; v a r c = 9 7 - 1 ; r s . _ r e a d = f u n c t i o n ( ) { i f ( c > = ' z ' . c h a r C o d e A t ( 0 ) ) r e t u r n r s . p u s h ( n u l l ) ; s e t T i m e o u t ( f u n c t i o n ( ) { r s . p u s h ( S t r i n g . f r o m C h a r C o d e ( + + c ) ) ; } , 1 0 0 ) ; } ; r s . p i p e ( p r o c e s s . s t d o u t ) ; p r o c e s s . o n ( ' e x i t ' , f u n c t i o n ( ) { c o n s o l e . e r r o r ( ' \ n _ r e a d ( ) c a l l e d ' + ( c - 9 7 ) + ' t i m e s ' ) ; } ) ; p r o c e s s . s t d o u t . o n ( ' e r r o r ' , p r o c e s s . e x i t ) ;
14. STREAM HANDBOOK https://github.com/substack/stream-handbook
15. PROMISES Come back next time and I promise to tell you what they are.
16. WHAT IS A PROMISE ? AND ABSTRACTION FOR ASYNC PROGRAMMING THAT PROXIES THE ASYNC CODE - KRIS KOWAL (Q)
17. CLEANER READING v a r p r o m i s e = d o S o m e t h i n g A y n c ( ) p r o m i s e . t h e n ( o n F u l f i l l e d , o n R e j e c t e d ) d o S o m e t h i n g A y n c ( f u n c t i o n ( e r r , d a t a ) { / / h a n d l e s t u f f h e r e } )
18. EVEN CLEANER v a r p r o m i s e = d o S o m e t h i n g A y n c ( ) . t h e n ( d o A n o t h e r A s y n c T h i n g ) . t h e n ( a n d A n o t h e r A s y n c T h i n g ) . t h e n ( a n d A l s o A s y n c T h i n g ) d o S o m e t h i n g A y n c ( f u n c t i o n ( r e s u l t s ) { d o A n o t h e r A s y n c T h i n g ( f u n c t i o n ( f u n c t i o n ( r e s u l t s ) { a n d A n o t h e r A s y n c T h i n g ( f u n c t i o n ( f u n c t i o n ( r e s u l t s ) { a n d A l s o A s y n c T h i n g ( f u n c t i o n ( f u n c t i o n ( r e s u l t s ) { / / h a n d l e s t u f f h e r e } ) } ) } ) } )
19. MAKING A PROMISE f u n c t i o n f s _ r e a d F i l e ( f i l e , e n c o d i n g ) { v a r d e f e r r e d = Q . d e f e r ( ) f s . r e a d F i l e ( f i l e , e n c o d i n g , f u n c t i o n ( e r r , d a t a ) { i f ( e r r ) d e f e r r e d . r e j e c t ( e r r ) / / r e j e c t s t h e p r o m i s e e l s e d e f e r r e d . r e s o l v e ( d a t a ) / / f u l f i l l s t h e p r o m i s e } ) r e t u r n d e f e r r e d . p r o m i s e / / t h e p r o m i s e i s r e t u r n e d } f s _ r e a d F i l e ( ' m y f i l e . t x t ' ) . t h e n ( c o n s o l e . l o g , c o n s o l e . e r r o r )
20. REFS Q : https://github.com/kriskowal/q Promises / A+ : http://promises-aplus.github.io/promises-spec/
21. THE END LEN WEINCIER LEN@CLOUDAFRICA.NET @CLOUDAFRICA