var, let, const and immutable of JavaScript

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1. ઌͣconstΑΓ࢝ΊΑ @arayaryoma 2018/08/20 - ϔϚλΠτࣾ಺LT

2. ٱʑʹJavaScriptॻ͚͘ͲES2015ͱ͔ ͍͏΍ͭͰ͍Ζ͍ΖมΘͬͯΔͬΆ͍ʁ ม਺એݴ࣌ɺvar ͚ͩ͡Όͳͯ͘let΋࢖͑Δʁ var͸ม਺ͩ͠let͸ఆ਺ͬΆ͍…ʁ Μɺconst΋͋Δʁ ΋͔ͯ͠͠ࢲͷJavaScriptɺ3೥஗ΕͯΔʁ

3. ٱʑʹJavaScriptॻ͚͘ͲES2015ͱ͔ ͍͏΍ͭͰ͍Ζ͍ΖมΘͬͯΔͬΆ͍ʁ ม਺એݴ࣌ɺvar ͚ͩ͡Όͳͯ͘let΋࢖͑Δʁ var͸ม਺ͩ͠let͸ఆ਺ͬΆ͍…ʁ Μɺconst΋͋Δʁ ΋͔ͯ͠͠ࢲͷJavaScriptɺ3೥஗ΕͯΔʁ ࠓ೔͸ͦΜͳ͋ͳͨͷͨΊʹ
 varͱletͱconstͷҧ͍Λ ղઆ͠·͢

4. ٱʑʹJavaScriptॻ͚͘ͲES2015ͱ͔ ͍͏΍ͭͰ͍Ζ͍ΖมΘͬͯΔͬΆ͍ʁ ม਺એݴ࣌ɺvar ͚ͩ͡Όͳͯ͘let΋࢖͑Δʁ var͸ม਺ͩ͠let͸ఆ਺ͬΆ͍…ʁ Μɺconst΋͋Δʁ ΋͔ͯ͠͠ࢲͷJavaScriptɺ3೥஗ΕͯΔʁ ͜ͷεϥΠυΛݟऴΘΔࠒ ͋ͳͨ͸varΛॻ͔ͳ͍਎ମʹ ͳ͍ͬͯΔͰ͠ΐ͏

5. ࿩͢͜ͱͱ݁࿦ JSͷvar, let, constͷҧ͍ͱ࢖͍ॴ ϞμϯͳJSͷॻ͖ํ(ྲྀߦ)ʹ͍ͭͯগ͚ͩ͠ var͸׬શʹෆཁ ·ͣ͸constͰॻ͘

6. redeclaration(࠶એݴ)

7. var let const

8. ಈ͘ʁ

9. ಈ͘(variable shadowing)

10. const΋ಉ͡ ಈ͕͘Մಡੑ͕Լ͕ΔͷͰආ͚Δ΂͖

11. scope(ม਺είʔϓ)

12. varͰએݴͨ͠ม਺ͷείʔϓ͸function಺ (τοϓϨϕϧʹએݴͨ͠৔߹͸άϩʔόϧ)

13. if(){}ͳͲͷϒϩοΫ಺Ͱએݴͨ͠ม਺Λ ϒϩοΫͷ֎͔ΒࢀরͰ͖Δ

14. letͰએݴͨ͠ม਺͸είʔϓ͕ϒϩοΫ಺

15. const΋ಉ͘͡ϒϩοΫείʔϓ

16. switch-caseͷ᠘

17. blockʹͯ͠ղܾ

18. reassign(࠶୅ೖ)

19. var͸࠶୅ೖՄೳ

20. let΋࠶୅ೖՄೳ

21. const͸࠶୅ೖෆՄೳ

22. ͨͩ͠constͰએݴͯ͠΋immutableͰ͸ͳ͍ͷͰ஫ҙɻ Objectͷproperty΍Arrayͷཁૉ͸͍͘ΒͰ΋ॻ͖׵ΘΔɻ

23. var let const ࠶એݴ είʔϓ function block block ࠶୅ೖ immutable?


    (primitiveͳσʔλܕҎ֎) NO NO NO

24. ࣮ફྫͰݟΔ
 ݱ୅෩JavaScript

25. ࣮ફྫ1 Array [1,2,3,4,5]ͷ֤ཁૉΛ10ഒͯ͠ग़ྗ

26. Bad. i͕for blockͷ֎ʹ΋ӨڹΛٴ΅͢

27. iͷείʔϓ͕for block಺ʹͳͬͨɻ
 Ͱ΋΋͏ͪΐͬͱ؆ܿʹॻ͖͍ͨɻ
 arrͷཁૉΛॻ͖׵͑ͯΔͷ΋ා͍ɻ

28. ࣮૷͸1ߦ
 arrΛมߋ͠ͳ͍ɻGood

29. ࣮ફྫ2 Array [1,2,3,4,5]ͷ֤ཁૉͷ߹ܭ஋Λग़ྗ

30. letͱfor loop

31. for-ofΛ࢖͏

32. Array.prototype.reduceΛ࢖͏ɻ
 sumΛ࠶୅ೖෆՄʹͰ͖ͯ҆શɻ

33. ݱ୅෩JS ม਺είʔϓ͸Ͱ͖Δ͚ͩখ͘͞ɺͰ͖Δ͚ͩ࠶୅ೖෆՄʹ͢Δ Ұ౓࡞ͬͨobject͸มԽͤ͞ͳ͍ͷ͕ਖ਼ٛ ෭࡞༻ͷൃੜΛආ͚Δ Immutable.jsΛ࢖ͬͯcollection͸͢΂ͯimmutableͰ͋Δ͜ͱΛલఏʹ͢Δ ྲྀ೿ ArrayͳͲʹศརͳmethod΋࢓༷Ͱ௥Ճ͞Ε͍ͯΔ(https://github.com/tc39/ proposals)

34. ࣮ફྫ3
 ඇಉظ+varͷා͞Λମݧ(ϥΠϒίʔσΟϯά)

35. Array΋Object΋immutableʹ͍ͨ͠ਓ΁

36. Object.freeze()ͰखܰʹObject΍ArrayΛimmutableʹ

37. Immutable.jsͷclassΛ࢖͏

38. Immutable.jsͬͯʁ https://facebook.github.io/immutable-js/ WebϑϩϯτΤϯυͰ͸͓ೃછΈͷFacebook੡ JavaScriptͰimmutableͳܕΛѻ͑ΔΑ͏ʹ͢ΔͨΊͷϥΠϒϥϦ Object΍ArrayͳͲɺJavaScriptͷbuilt-inͳσʔλܕΛimmutableʹ ͢ΔΞϓϩʔνͰ͸ͳ͘ɺؔ਺ܕݴޠ͔Β༌ೖͨ͠ಠࣗͷσʔλܕ Λѻ͏ List, Stack, Map,

    OrderedMap, Set, OrderedSet,

39. ·ͱΊ var͸΋͏͍Βͳ͍ ·ͣconstͰॻ͍ͯɺͲ͏ͯ͠΋ඞཁͳΒletΛ࢖͏ ෭࡞༻Λආ͚Δ͜ͱ͕ਖ਼ٛͩͱ͍͏࣌୅ ؔ਺ܕݴޠͷύϥμΠϜ͕JSͷੈքʹ༌ೖ͞ΕͯΔ TypeScript + Rx.js + Immutable.jsͱ͔΍Γ͸͡ΊΔͱ׬શʹผݴޠ