Lessons learned from node.js. Node.js methodology, working with callbacks, using promises. If you ever decide to one day sit down and write in node.js just remember to use promises. Instead of calling a passed callback, return a promise.

1. Lessons Learned
from Node.js
Jason Yau
Director of Engineering
Samsung Accelerator
Tuesday, October 8, 13

2. 1. Node.js
2. Methodology
3. Callbacks
4. Promises
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3. Node.js is javascript
on the server side.
It’s event-driven, non-
blocking I/O model
makes it FAST and
scalable.
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4. Tuesday, October 8, 13

5. In most languages,
the code we write is
synchronous.
aka Blocking
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6. Blocking
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7. Waiting
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8. In javascript, we do
things differently;
asynchronously.
aka Non-blocking
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9. Non-Blocking
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10. Parallel
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11. Fast
http://benchmarksgame.alioth.debian.org/u64/benchmark.php?test=all&lang=v8&lang2=yarv&data=u64
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12. Javascript
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13. Popular
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14. Methodology
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15. I/O Latency
• L1: 3 cycles
• L2: 14 cycles
• RAM: 250 cycles
• DISK: 41,000,000 cycles
• NETWORK: 240,000,000 cycles
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16. A theoretical request.
Request Process Results
Query DB or Web Service Write to log file
Format Response
= blocking / waiting
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17. Scale with Threads
Scale with Processes
Thread 1
Thread 2
Thread 3
Thread 4
Process 1
Process 2
Process 3
Process 4
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18. Scale with Event Loop
Handles many concurrent requests in a single
process / thread
Process 1
Thread Pool
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19. Analogy
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20. Event Queue Thread Pool
Event Loop
Filesystem
Network
Process
Other
Scale with Event Loop
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21. Challenges with
Callbacks
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22. Recurring Question
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23. Callbacks Example
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24. Pyramid of Doom
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25. Debugging
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26. Parallel Example
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27. Promises
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28. What are promises?
A promise is an object that represents a one-time
event, typically the outcome of an async task like an
AJAX call. When a promise is returned, at first it is in a
pending state.
Eventually it’s either:
1. resolved - The promise is fulfilled with a value
2. rejected - The promise is broken
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29. Instead of calling a
passed callback,
return a promise.
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30. Callback example
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31. Return a promise
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32. Passed callback
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33. Return a promise
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34. Parallel I/O
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35. Promises are cleaner
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36. Instead of calling a
passed callback,
return a promise.
Promise me you’ll
remember promises.
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37. Thank You
Jason Yau
Director of Engineering, Samsung
work: jason@samsungaccelerator.com
Tuesday, October 8, 13