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JAVASCRIPT REFERENCES & VALUES

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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

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References and Values ࢀর ஋

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References and Values ஋ ஋ ࢀর ࢀর

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References and Values ࢀর͸ؒ઀తʹΦϒδΣΫτΛมߋ͢Δ ஋͸௚઀ͦͷΦϒδΣΫτΛมߋ͢Δ

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References or Values? KBWBTDSJQU͸ࢀরͱ஋ͷ྆ํΛ࢖͏ ΦϒδΣΫτຖʹͲ͏ѻΘΕΔ͔ܾ·͍ͬͯΔ

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Javascript object traits ࢀর "MMWBMVFTFYUFOET0CKFDU ஋ TUSJOH OVNCFS CPPMFBO

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Pass by reference/value const A = const B = ࢀর ஋ A = B = ஋

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Pass by reference const A = {}; const B = A; B.x = 1; console.log(A); // { x: 1 }

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Pass by value const A = 1; const B = A; B++; console.log(A); // 1

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Until here… ͱɺ͜͜·Ͱ͕Α͘ݴΘΕ͍ͯΔ ࠓճ͸΋͏ͪΐ͍ਂ۷Γͯ͠Έ͍ͨ

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Mutable, Immutable KBWBTDSJQUʹ͸ มߋՄೳͳ஋ͱมߋෆՄೳͳ஋͕͋Δ TUSJOH OVNCFS CPPMFBO͸มߋͰ͖ͳ͍

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Special cases OVNCFSͱCPPMFBO͸஋౉͠Ͱ͋Δ͜ͱ͕ଟ͍ ͨͩ͠TUSJOH͸৭ʑͳ޻෉͕͋Δέʔε͕ଟ͍ 7Ͱ͸TUSJOH͸ࢀরͱͳ͍ͬͯΔ

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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;

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Immutablity make reference to value *NNVUBCMFͳจࣈྻ͕஋ͷΑ͏ʹৼΔ෣͏͕ ࣮ࡍʹ͸͢΂ͯࢀরΛ౉͍ͯ͠Δ

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What is reference? ࢀরͱ͸ͳΜͩΖ͏

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Pointer ΦϒδΣΫτ͸ੜ੒͞ΕΔͱώʔϓྖҬͱ͍͏ϝ ϞϦʹׂΓ౰ͯΒΕΔ ͦͷΦϒδΣΫτΛૢ࡞͢Δ৔߹͸ͦͷϝϞϦྖ ҬΛࢦࣔ͢͠ΞυϨεΛඞཁͱ͢Δ ͜Ε͕ϙΠϯλͱݺ͹ΕΔ΋ͷ

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Pointer is value KTΤϯδϯΛ࣮૷͍ͯ͠Δ$$ͷੈքͰ͸ ϙΠϯλͦͷ΋ͷ΋·ͨ஋Ͱ͋Δ ͦͷͨΊϙΠϯλͷϙΠϯλΛ࡞ͬͨΓ΋Ͱ͖Δ

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Reference is value ͔͠͠KBWBTDSJQUͷੈքͰ͸ࢀরͷࢀর͸࡞Εͳ͍ ͭ·Γࢀর͸ৗʹ஋౉͠ͱͳΔ

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pass by copy reference ͭ·ΓKBWBTDSJQUͰ͸ ࢀর ϙΠϯλ Λ஋౉͍ͯ͠͠Δ ࢀরͷ஋౉͠ͱͳ͍ͬͯΔ

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Appendix 7಺෦ͷจࣈྻ࣮૷Λ؆୯ʹ

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String in V8 7Ͱ͸จࣈྻ͕ҎԼͷΫϥεʹ෼͔Ε͍ͯΔ 4FR0OF#ZUF4USJOH 4FR5XP#ZUF4USJOH $POT4USJOH 5IJO4USJOH 4MJDFE4USJOH

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String in V8 ಛʹTVCTUSJOHΛߦͬͨΓͯ͠ ৽ͨʹจࣈྻΠϯελϯεΛ࡞੒͢Δ৔߹ 3PQFͱ͍͏ΞϧΰϦζϜΛར༻ͨ͠ $POT4USJOH͕ར༻͞ΕΔ

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Rope จࣈྻͷ݁߹͕ߴ଎0 MPHO ෼ׂ΋ߴ଎0 MPHO औΓग़͠0 MPHO

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Rope 5PEBZJTXFBSFKBWBTDSJQUFS`T 5PEBZJT XFBSFKBWBTDSJQUFS`T 3005

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Rope 5PEBZJT 3005 8FBSF KBWBTDSJQUFS`T 53&&

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Summary ࢀরͱ஋͔Β3PQF·ͰோΊͯΈ·ͨ͠ ͝ਗ਼ௌ͋Γ͕ͱ͏͍͟͝·ͨ͠