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javascriptの参照と値
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Taketoshi Aono(青野健利 a.k.a brn)
October 23, 2018
2
870
javascriptの参照と値
javascriptの参照渡しと値渡しについて
Taketoshi Aono(青野健利 a.k.a brn)
October 23, 2018
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Transcript
JAVASCRIPT REFERENCES & VALUES
Name @brn (⻘野健利) Occupation フロントエンドエンジニア・ネイティブエンジニア Company Cyberagent アドテクスタジオ AI Messenger
OSS Contributor of V8 About http://info.b6n.ch
References and Values ࢀর
References and Values ࢀর ࢀর
References and Values ࢀরؒతʹΦϒδΣΫτΛมߋ͢Δ ͦͷΦϒδΣΫτΛมߋ͢Δ
References or Values? KBWBTDSJQUࢀরͱͷ྆ํΛ͏ ΦϒδΣΫτຖʹͲ͏ѻΘΕΔ͔ܾ·͍ͬͯΔ
Javascript object traits ࢀর "MMWBMVFTFYUFOET0CKFDU TUSJOH OVNCFS CPPMFBO
Pass by reference/value const A = const B = ࢀর
A = B =
Pass by reference const A = {}; const B =
A; B.x = 1; console.log(A); // { x: 1 }
Pass by value const A = 1; const B =
A; B++; console.log(A); // 1
Until here… ͱɺ͜͜·Ͱ͕Α͘ݴΘΕ͍ͯΔ ࠓճ͏ͪΐ͍ਂ۷Γͯ͠Έ͍ͨ
Mutable, Immutable KBWBTDSJQUʹ มߋՄೳͳͱมߋෆՄೳͳ͕͋Δ TUSJOH OVNCFS CPPMFBOมߋͰ͖ͳ͍
Special cases OVNCFSͱCPPMFBO͠Ͱ͋Δ͜ͱ͕ଟ͍ ͨͩ͠TUSJOH৭ʑͳ͕͋Δέʔε͕ଟ͍ 7ͰTUSJOHࢀরͱͳ͍ͬͯΔ
String behave like value let A = 'a'; let B
= A; A += 'b' // Create new instance and assign to self. console.log(A); // 'ab'; console.log(B); // 'a;
Immutablity make reference to value *NNVUBCMFͳจࣈྻ͕ͷΑ͏ʹৼΔ͏͕ ࣮ࡍʹͯ͢ࢀরΛ͍ͯ͠Δ
What is reference? ࢀরͱͳΜͩΖ͏
Pointer ΦϒδΣΫτੜ͞ΕΔͱώʔϓྖҬͱ͍͏ϝ ϞϦʹׂΓͯΒΕΔ ͦͷΦϒδΣΫτΛૢ࡞͢Δ߹ͦͷϝϞϦྖ ҬΛࢦࣔ͢͠ΞυϨεΛඞཁͱ͢Δ ͜Ε͕ϙΠϯλͱݺΕΔͷ
Pointer is value KTΤϯδϯΛ࣮͍ͯ͠Δ$$ ͷੈքͰ ϙΠϯλͦͷͷ·ͨͰ͋Δ ͦͷͨΊϙΠϯλͷϙΠϯλΛ࡞ͬͨΓͰ͖Δ
Reference is value ͔͠͠KBWBTDSJQUͷੈքͰࢀরͷࢀর࡞Εͳ͍ ͭ·Γࢀরৗʹ͠ͱͳΔ
pass by copy reference ͭ·ΓKBWBTDSJQUͰ ࢀর ϙΠϯλ Λ͍ͯ͠͠Δ ࢀরͷ͠ͱͳ͍ͬͯΔ
Appendix 7෦ͷจࣈྻ࣮Λ؆୯ʹ
String in V8 7Ͱจࣈྻ͕ҎԼͷΫϥεʹ͔Ε͍ͯΔ 4FR0OF#ZUF4USJOH 4FR5XP#ZUF4USJOH $POT4USJOH 5IJO4USJOH 4MJDFE4USJOH
String in V8 ಛʹTVCTUSJOHΛߦͬͨΓͯ͠ ৽ͨʹจࣈྻΠϯελϯεΛ࡞͢Δ߹ 3PQFͱ͍͏ΞϧΰϦζϜΛར༻ͨ͠ $POT4USJOH͕ར༻͞ΕΔ
Rope จࣈྻͷ݁߹͕ߴ0 MPHO ׂߴ0 MPHO औΓग़͠0 MPHO
Rope 5PEBZJTXFBSFKBWBTDSJQUFS`T 5PEBZJT XFBSFKBWBTDSJQUFS`T 3005
Rope 5PEBZJT 3005 8FBSF KBWBTDSJQUFS`T 53&&
Summary ࢀরͱ͔Β3PQF·ͰோΊͯΈ·ͨ͠ ͝ਗ਼ௌ͋Γ͕ͱ͏͍͟͝·ͨ͠