From: http://gotocon.com/aarhus-2013/presentation/Why%20code%20in%20Node.js%20often%20gets%20rejected%20by%20SoundCloud At SoundCloud we ask candidates to send us some code before inviting them in for interviews. Candidates can use whatever language they want, and over the past years we saw a massive rise on the number of submissions using server-side JavaScript. Unfortunately, too many submissions are asynchronous blobs of procedural code. JavaScript is a fairly functional language, and over the past decades Functional Programming developed interesting solutions for many of the problems we face when writing Node.js and regular JavaScript. Let's talk about how to leverage good old Functional Programming techniques to make code less coupled and more readable!

1. Why code in Node.js
often get rejected by
SoundCloud
Phil Calçado - SoundCloud
@pcalcado
http://philcalcado.com
Tuesday, October 1, 13

2. 2011: Phil zieht nach Berlin
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3. Tuesday, October 1, 13

4. ~ 200 million users / month
> 11 hours of audio
uploaded every minute
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5. Tuesday, October 1, 13

6. http://bit.ly/15DToNK
hiring @ SoundCloud
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7. Phone
Code Review
Interviews
Offer
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8. Phone
Code Review
Interviews
Offer
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9. challenge until late 2012
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10. you can choose any language.
0
10
20
30
40
Ruby Java JavaScript (Node.js) C Clojure Scala
% of submissions ~2011-2012
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11. you can choose any language.
0
10
20
30
40
Ruby Java JavaScript (Node.js) C Clojure Scala
rejected before interview invited for inverview
Tuesday, October 1, 13

12. new challenge
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13. you can choose any language.
0
7.5
15
22.5
30
Ruby Java JavaScript (Node.js) Go Clojure Scala
% of submissions on the past ~1 year
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14. you can choose any language.
0
7.5
15
22.5
30
Ruby Java JavaScript (Node.js) Go Clojure Scala
% of submissions on the past ~1 year
Tuesday, October 1, 13

15. you can choose any language.
0
7.5
15
22.5
30
Ruby Java JavaScript (Node.js) Go Clojure Scala
rejected before interview invited for inverview
Tuesday, October 1, 13

16. you can choose any language.
0
7.5
15
22.5
30
Ruby Java JavaScript (Node.js) Go Clojure Scala
rejected before interview invited for inverview
WTF?
Tuesday, October 1, 13

17. http://bit.ly/J1aLNn
don’t get me wrong
we are all hipsters
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18. Tuesday, October 1, 13

19. Not OO, not Functional...
Just (bad) Procedural code.
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20. http://bit.ly/JiECRp
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21. we don’t need this complicated stuff.
this is not java, you know.
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22. http://bit.ly/JiFSnq
so how do we structure our app?
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23. what to use?
(decent)
procedures?
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24. Tuesday, October 1, 13

25. Tuesday, October 1, 13

26. what to use?
objects?
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27. Tuesday, October 1, 13

28. what to use?
...functions?
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29. http://bit.ly/JFbZt8
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30. http://bit.ly/JFbZt8
“SICP and some of the Sussman & Steele "Lambda
the ..." papers made a big impression on me years
before, although I did not understand their full
meaning then.
Remember, I was recruited to "do Scheme" [...] My
interest in languages such as Self informed a
subversive agenda [...]. Likewise with first-class
functions, which were inspired by Scheme [...]”
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31. http://bit.ly/JiEQYM
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32. Tuesday, October 1, 13

33. Tuesday, October 1, 13

34. Tuesday, October 1, 13

35. Tuesday, October 1, 13

36. Tuesday, October 1, 13

37. http://bit.ly/JiF7ef
going old school
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38. e.g. passing functions around
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39. we see a lot of this
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40. 1st, we extract what is common
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41. then we refactor our functions
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42. and we send them as arguments
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43. e.g. closures not only for objects
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44. we see a lot of this
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45. we can keep writeComment as it is
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46. and we add a function with two closures
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47. and we add a function with two closures
immutable
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48. and we add a function with two closures
immutablemutable
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49. now we don’t need to pass in the kitchen sink
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50. e.g. functions all the way down
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51. we see a lot of this
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52. first we extract common protocol
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53. then we clean up our functions
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54. then we use them.
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55. then we use them. redundant?
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56. http://bit.ly/JiETnd
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57. our “framework”:
1 - Extract protocol in
“combinators”
2 - Keep mutable state in
closures
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58. no scary monads required
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59. there is plenty to learn from
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60. in the javascript community too
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61. phil calçado
http://philcalcado.com
@pcalcado
www.soundcloud.com
Tuesday, October 1, 13

62. How to Design Programs - http://bit.ly/K0BfrL
Structure and Interpretation of Computer
Programs - http://bit.ly/K0BjYm
The Art of the Metaobject Protocol
http://amzn.to/K0BqU1
Purely Functional Data Structures
http://amzn.to/JFn4KG
Let Over Lambda - http://amzn.to/IMMkNO
An Introduction to Lambda Calculi for Computer
Scientists - http://amzn.to/IX8d1B
All drawings are available as t-shirts from the
awesome Diesel Sweeties -
http://dieselsweeties.com/
Tuesday, October 1, 13