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JavaScriptの読み込みを考える〜場所、async、defer、その仕組みと使い所〜
Masayuki Maekawa
November 16, 2019
Technology
3
1.7k
JavaScriptの読み込みを考える〜場所、async、defer、その仕組みと使い所〜
フロントエンドカンファレンス福岡 2019
https://frontend-conf.fukuoka.jp/
セッション資料です。
Masayuki Maekawa
November 16, 2019
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Transcript
+BWB4DSJQUͷ ಡΈࠐΈΛߟ͑Δ גࣜձࣾΦϛΧϨɹલণ ॴɺ BTZODɺ EFGFSɺ ͦͷΈͱ͍ॴ
ࠓͷ͓
+BWB4DSJQUΣϒϖʔδʹ͔ܽͤͳ͍ଘࡏʹ ͳ͍ͬͯ·͕͢ɺ ϖʔδͷදࣔͷύϑΥʔϚϯεΛ ߟ͑ΔࡍʹԿ͔ͱΛΒΜͰ͍Δ ଘࡏʹͳ͍ͬͯ·͢ɻ ͦͷͨΊɺ ύϑΥʔϚϯε্ͷͨΊʹ༷͕ࡦఆ͞Εɺ ϒϥβଆରԠΛਐΊ͍ͯ·͢ɻ
͜ͷηογϣϯͰɺ ύϑΥʔϚϯε্ͷͨΊͷ ঢ়گʹ͍ͭͯཧ͠ɺ খʙதنͷΣϒαΠτɺ ΣϒΞϓϦέʔγϣϯ Λ࡞͍ͯ͠Δਓʹɺ දࣔͷ࠷దԽͷҰॿͱͯ͠ +BWB4DSJQUͷಡΈࠐΈʹ͍ͭͯղઆ͠·͢ɻ
ࣗݾհ લণ ʢ·͔͑Θ·͞Ώ͖ʣ גࣜձࣾΦϛΧϨ 69σϕϩούʔ !NBFQPO
None
ࠗ׆ͱ͍͑ΦϛΧϨ
͡Ί·͢
+BWB4DSJQUΣϒϖʔδʹ͔ܽͤͳ͍ଘࡏʹ ͳ͍ͬͯ·͕͢ɺ ϖʔδͷදࣔͷύϑΥʔϚϯεΛ ߟ͑ΔࡍʹԿ͔ͱΛΒΜͰ͍Δ ଘࡏʹͳ͍ͬͯ·͢ɻ ͦͷͨΊɺ ύϑΥʔϚϯε্ͷͨΊʹ༷͕ࡦఆ͞Εɺ ϒϥβଆରԠΛਐΊ͍ͯ·͢ɻ
+BWB4DSJQUͱදࣔύϑΥʔϚϯεͷؔ
ΫϥΠΞϯτ ʢϒϥβʣ ͕ड͚औΔ લ ޙ
ΫϥΠΞϯτ ʢϒϥβʣ ͕ड͚औΔ લ ޙ w ϦΫΤετͷλΠϛϯά w ωοτϫʔΫͷঢ়ଶ
w ϑΝΠϧͷαΠζ w ϑΝΠϧͷ w FDUʜ w ࣮ߦͷλΠϛϯά w ϓϩάϥϜͷෛՙ w %0.ͷෛՙ w FDUʜ
ΫϥΠΞϯτ ʢϒϥβʣ ͕ड͚औΔ લ ޙ w ϦΫΤετͷλΠϛϯά w ωοτϫʔΫͷঢ়ଶ
w ϑΝΠϧͷαΠζ w ϑΝΠϧͷ w FDUʜ w ࣮ߦͷλΠϛϯά w ϓϩάϥϜͷෛՙ w %0.ͷෛՙ w FDUʜ ࠓճͷͰؔΘͬͯ͘Δͷ͜͜
$ISPNFͷ%FW5PPMTͷ ʮ1FSGPSNBODFʯ Ͱͦͷ͋ͨΓ͕͑·͢ɻ
None
+BWB4DSJQUΣϒϖʔδʹ͔ܽͤͳ͍ଘࡏʹ ͳ͍ͬͯ·͕͢ɺ ϖʔδͷදࣔͷύϑΥʔϚϯεΛ ߟ͑ΔࡍʹԿ͔ͱΛΒΜͰ͍Δ ଘࡏʹͳ͍ͬͯ·͢ɻ ͦͷͨΊɺ ύϑΥʔϚϯε্ͷͨΊʹ༷͕ࡦఆ͞Εɺ ϒϥβଆରԠΛਐΊ͍ͯ·͢ɻ
<script type=“text/javascript src=“foo.js” async> <script type=“text/javascript src=“bar.js” defer> BTZODͱEFGFS
ैདྷͷ+4ಡΈࠐΈ +4ಡΈࠐΈ +4࣮ߦ )5.-ύʔε
)5.-ύʔε BTZOD +4ಡΈࠐΈ +4࣮ߦ
BTZODͷK2VFSZͷͨΊʹɺ 1BSTF)5.-͕தஅ͞Ε͍ͯ·͢
EFGFS +4ಡΈࠐΈ +4࣮ߦ )5.-ύʔε %0.$POUFE-PBEFE
BTZOD w ಡΈࠐΈ͕ྃͨ͠εΫϦϓτ͔Β࣮ߦ w )5.-ͷهड़ͷॱ൪ʹ߆ଋ͞Εͳ͍
<script src=“jQuery.js” async> <script src=“jquery-plugin.js” async> ͜ͷ߹ɺ ΤϥʔʹͳΔՄೳੑ͕ͱͯߴ͍
EFGFS w )5.-ͷهड़ͷॱ൪Ͱ࣮ߦ
<script src=“jQuery.js” defer> <script src=“jquery-plugin.js” defer> ͜ͷهड़ͷ߹ΤϥʔʹͳΒͳ͍
<script src=“jQuery.js” async> <script src=“jquery-plugin.js” defer> ΤϥʔͷՄೳੑ͋Γ
ҙ ಡΈࠐΉ+BWB4DSJQUʹґଘͨ͠ +BWB4DSJQU͕CPEZʹ TDSJQUλάͱͯ͠هड़͞Ε͍ͯΔ߹ɺ BTZODEFGFS͑ͳ͍
<script src=“jQuery.js”> <script src=“jquery-plugin.js” defer> ͜͏ͳΔ
BTZODͱEFGFS ࣮ߦλΠϛϯάͷҧ͍͋Δ͕ɺ ϑΝΠϧͷಡΈࠐΈΛඇಉظͰߦ͑ΔͷͰ ͦͷؒɺ )5.-ͷύʔεΛ્͠ͳ͍
+BWB4DSJQUΣϒϖʔδʹ͔ܽͤͳ͍ଘࡏʹ ͳ͍ͬͯ·͕͢ɺ ϖʔδͷදࣔͷύϑΥʔϚϯεΛ ߟ͑ΔࡍʹԿ͔ͱΛΒΜͰ͍Δ ଘࡏʹͳ͍ͬͯ·͢ɻ ͦͷͨΊɺ ύϑΥʔϚϯε্ͷͨΊʹ༷͕ࡦఆ͞Εɺ ϒϥβଆରԠΛਐΊ͍ͯ·͢ɻ
Ͳ͏͍ͯ͜͠͏͔ʁ
ಡΈࠐΈͷඇಉظԽ w ࠷ݶɺ ϑΝΠϧऔಘ࣌ͷϒϩοΫΛͳ͘͢ w CPEZͷϥΠϒϥϦͳͲʹґଘͨ͠ +BWB4DSJQU໓͢Δ
BTZODͱEFGFSɺ Ͳͬͪʁ
Ͳͬͪʁ
έʔε ɾ όΠ ɾ έʔε ʂ
)5.-ύʔε BTZOD +4ಡΈࠐΈ +4࣮ߦ
)5.-ύʔε BTZOD +4ಡΈࠐΈ +4࣮ߦ ͕͜͜ؾʹͳΔ
ͱ͍͑ʜ
EFGFS +4ಡΈࠐΈ +4࣮ߦ )5.-ύʔε %0.$POUFE-PBEFE
EFGFS +4ಡΈࠐΈ +4࣮ߦ )5.-ύʔε %0.$POUFE-PBEFE ͕͜͜ौ͢Δͷ
BTZOD͕͍͍ͯΔͷ w ϢʔβʔτϥοΩϯάܥ w %0.ΑΓԼͷϨΠϠʔΛѲΔͷ
EFGFS͕͍͍ͯΔͷ w 6*ૢ࡞ܥ w %-$ %0.$POUFOU-PBEFE ͰൃՐ͢Δͷ
BTZODͱEFGFS ͲͷΑ͏ͳతͷεΫϦϓτ͔Λߟ͑ͯબ
ͱ͜ΖͰʜ
TDSJQUͲ͜Ͱॻ͍ͯ·͢ʁ
+4ͷಡΈࠐΈ ʮCPEZͷલʹ+4ΛಡΈࠐΉʯ ͷੋඇ
BTZODEFGFSΛCPEZલʹஔ͘ͱʜ +4ಡΈࠐΈ +4࣮ߦ )5.-ύʔε
+4ͷಡΈࠐΈ ඇಉظಡΈࠐΈͷಛੑ͕ߦ͔ͤͳ͍ͷͰɺ IFBEIFBE͕ྑ͍ͷͰʁ
·ͱΊ
ݪଇͱͯ͠ w TDSJQUʹ ʮEFGFSʯ ͘͠ ʮBTZODʯ Λ͚ͭΔ w ͲͪΒ͔తΛ͔Βஅ͢Δ w
ͦͷ্ͰIFBEIFBEʹ
࠷ޙʹ ͜ͷ͓දࣔ࠷దԽͷͨΊͷখ͞ͳϐʔε
࠷ޙʹ ࠓҰௌ͍ͨ͞·͟·ͳͷΛ࣋ͪؼͬͯ
࠷ޙʹ շదͳΣϒΛϢʔβʔʹಧ͚·͠ΐ͏ ʂ
ࠗ׆ͱ͍͑ΦϛΧϨ ͋Γ͕ͱ͏͍͟͝·ͨ͠ ʂ !NBFQPO