Callback to Promise and beyond

$BMMCBDLUP1SPNJTFBOECFZPOE
d1SPNJTFԽ͚ͩͰ͸ऴΘΒͳ͍d
೥݄೔ؔ੢/PEFֶԂ࣌ݶ໨
Ϡϑʔגࣜձࣾɹ܀ࢁଠر

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ࣗݾ঺հ
܀ࢁଠرʢ!"KJEPʣ
Ϡϑʔגࣜձࣾ›/PEFKTࠇଳ

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w $BMMCBDLΛ1SPNJTFԽ͢Δํ๏
w $BMMCBDLΛ1SPNJTFԽͨ͠ޙʹ࢒Δ՝୊
w ੑೳ›ݱ୅తͳϑϩʔ੍ޚ͸ߴ଎ͳͷ͔ʁ
w ετϦʔϜରԠ›4USFBNΛϑϩʔ੍ޚʹͲ͏૊ΈࠐΉʁ
w Τϥʔॲཧ›ඇಉظॲཧͷελοΫτϨʔε͸Ͳ͏ݟ͑Δʁ
಺༰

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/PEFKTʹ͓͚Δඇಉظॲཧͱϑϩʔ੍ޚͷྺ࢙
"TZODUZQF /PEFWFSTJPO
$BMMCBDL
3FNPWFQSPNJTFT
W
BTZOD OQN

CMVFCJSE OQN
2 OQN

1SPNJTF" W 7

(FOFSBUPS W 7

"TZOD'VODUJPOT BTZODBXBJU
W 7

"TZOD*UFSBUJPO GPSBXBJUPG
&YQFSJNFOUBM

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BTZODBXBJUʹΑͬͯඇಉظॲཧͷϑϩʔ੍ޚ͸༰қʹͳ͕ͬͨɺ$BMMCBDLܕͷϝ
ιου͸1SPNJTFʹม׵͠ͳ͚Ε͹ϑϩʔ੍ޚʹ૊ΈࠐΉ͜ͱ͕Ͱ͖ͳ͍ɻ1SPNJTF
ʹରԠ͍ͯ͠ͳ͍ɺϑϩʔ੍ޚʹ૊Έࠐ·ΕΔͰ͋Ζ͏Ϟδϡʔϧ͸ҎԼͷ͍ͣΕ͔ͷ
બ୒ΛഭΒΕͨɻ
$BMMCBDLΛݱ୅తͳϑϩʔ੍ޚʹରԠͤ͞Δ
$BMMCBDLͷ··ܧଓ͢Δʢ1SPNJTFม׵͸ར༻ऀʹ೚ͤΔʣ
1SPNJTFʹ੾Γସ͑ɺޓ׵ੑΛࣺͯΔ
$BMMCBDLͱ1SPNJTFͷΠϯλʔϑΣʔεΛཱ྆ͤ͞Δ
બ୒

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$BMMCBDLΛলུͨ࣌͠ʹ1SPNJTFΛฦ͢
1SPNJTFઐ༻ͷΠϯλʔϑΣʔεΛ௥Ճ͢Δ
‣ 1SPNJTFܕͷϞδϡʔϧΛฦ͢
‣ ϝιουνΣʔϯ͔Β1SPNJTFΛฦ͢
‣ 4VGpY෇͖ͷؔ਺͔Β1SPNJTFΛฦ͢
Ϟδϡʔϧ಺Ͱ$BMMCBDLͱ1SPNJTFͷΠϯλʔϑΣʔεΛཱ྆ͤ͞Δํ๏ʹ͸͍ͭ͘
͔ͷબ୒ࢶ͕͋ΓɺͦΕͧΕʹϝϦοτͱσϝϦοτ͕ଘࡏ͢Δɻ

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$BMMCBDLͱ1SPNJTFͷཱ྆
$BMMCBDLΛলུͨ࣌͠ʹ1SPNJTF͕ฦΔ
// Callback
func((data) => {
console.log(data)
})
// Promise
const data = await func()
console.log(data)
ϚʔέοτΛௐࠪ͢ΔݶΓ͜ͷελΠϧͷ࠾༻ྫ͸ଟ͘ɺ+BWB4DSJQUͷจԽΛݟͯ΋
ύϥϝʔλΛলུͯ͠ڍಈ͕มΘΔ࢓૊Έ͸ଟ͘ଘࡏ͍ͯ͠Δɻ
ϝιου͝ͱͷஈ֊తͳ1SPNJTFԽ͕ՄೳͰɺকདྷతͳ$BMMCBDLͷഇࢭ΋ࢹ໺ʹೖ
Ε΍͍͢ɻͨͩ͠TFU5JNFPVU΍DIJME@QSPDFTTFYFDͷΑ͏ͳίʔϧόοΫؔ
਺Λड͚औΓɺಉ࣌ʹฦΓ஋΋ଘࡏ͢Δؔ਺ͱ͸૬ੑ͕ѱ͍ͨΊ஫ҙ͕ඞཁɻ

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1SPNJTFܕͷϞδϡʔϧΛฦ͢
// Callback
const fs = require('fs')
fs.readFile('/etc/hosts', (err, data) => {
console.log(data)
})
// Promise
const fs = require('fs').promises
const data = await fs.readFile('/etc/hosts')
console.log(data)
/PEFKTͷຊମ͕࠾༻͍ͯ͠Δํ๏ɻ͢΂ͯͷϝιουΛҰׅͰ1SPNJTFԽͰ͖Δͱ
͍͏ར఺͕͋Γɺ·ͨϞδϡʔϧͷ։ൃऀࢹ఺Ͱ͸طଘͷ$BMMCBDLؔ਺ʹखΛՃ͑Δ
ඞཁ͕ͳ͍ͱ͍͏ར఺΋͋Δɻ
͔͠͠Ϟδϡʔϧ಺ʹଘࡏ͢Δ͢΂ͯͷཁૉΛෳ੡ͯ͠վम͢Δඞཁ͕͋ΔͨΊɺରԠ
ͷίετ͸վम࣌ʹूத͢Δɻ

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ϝιουνΣʔϯ͔Β1SPNJTFΛฦ͢
// Callback
func((data) => {
console.log(data)
})
// Promise
const data = await func().promise()
console.log(data)
"844%,GPS+BWB4DSJQUͳͲ͕࠾༻͍ͯ͠Δํ๏ɻ1SPNJTFʹݶΒͣɺ4USFBN
ͷΑ͏ͳෳ਺ύλʔϯͷΠϯλʔϑΣʔεΛ໌ࣔతʹࢦఆͯ͠ฦ͢͜ͱ΋Ͱ͖Δɻ
طଘͷ$BMMCBDLؔ਺ʹखΛՃ͑Δඞཁ͕ͳ͍ͱ͍͏ར఺͕͋ΓɺϞδϡʔϧ಺ͷϝιο
υΛ෦෼తʹ1SPNJTFରԠ͍ͯ͘͜͠ͱ΋Ͱ͖Δ͕ɺকདྷతͳ$BMMCBDLͷഇࢭΛࢹ
໺ʹೖΕΔ৔߹͸ѻ͍͕೉͍͠ɻ

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4VGpY෇͖ͷؔ਺͔Β1SPNJTFΛฦ͢
// Callback
func((data) => {
console.log(data)
})
// Promise
const data = await funcAsync()
console.log(data)
VUJMQSPNJTJGZ΍CMVFCJSEQSPNJTJGZ"MMͳͲΛར༻͢Δ͜ͱʹΑͬͯɺ࠷খݶ
ͷίετͰϞδϡʔϧ಺ͷϝιουΛ1SPNJTFʹରԠ͢Δ͜ͱ͕Ͱ͖Δɻ
কདྷతͳ$BMMCBDLͷഇࢭΛߟ͑Δ৔߹ɺޓ׵ੑʹͲ͏ରॲ͢Δ͔͕೰·͍͠ɻ4VGpYΛ
ҡ࣋͢Δ͔ɺ·ͨ͸4VGpYΛআڈͯ͠1SPNJTFͷར༻ऀʹෛՙΛ༩͑Δ͔ͷબ୒͕ඞཁɻ

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֤ύλʔϯͷ۩ମతͳ࣮૷ํ๏͸ϒϩάͷهࣄ಺ʹɻ͓͢͢Ί͸ஈ֊తͳ1SPNJTFԽͱ
$BMMCBDLͷഇࢭΛࢹ໺ʹೖΕ΍͍͢ʮ$BMMCBDLΛলུͨ࣌͠ʹ1SPNJTFΛฦ͢ʯํ๏ɻ
$BMMCBDLΛলུͨ࣌͠ʹ1SPNJTFΛฦ͢
1SPNJTFઐ༻ͷΠϯλʔϑΣʔεΛ௥Ճ͢Δ
‣ 1SPNJTFܕͷϞδϡʔϧΛฦ͢
‣ ϝιουνΣʔϯ͔Β1SPNJTFΛฦ͢
‣ 4VGpY෇͖ͷؔ਺͔Β1SPNJTFΛฦ͢
ݸਓత͓͢͢Ί

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ੑೳ
ݱ୅తͳϑϩʔ੍ޚ͸ߴ଎ͳͷ͔ʁ

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%PY#FFϕϯνʔϚʔΫͰ/PEFW؀ڥͷ$BMMCBDLͱ1SPNJTFɺBTZOD
BXBJUͷύϑΥʔϚϯεΛܭଌ‎ݱ࣌఺Ͱ͸$BMMCBDL͕࠷଎
εϧʔϓοτΛՄࢹԽ͍ͯ͠ΔͨΊ௿͚Ε͹௿͍
΄ͲύϑΥʔϚϯε͕ߴ͍͜ͱΛද͢ɻ
$BMMCBDL͸ଞͷඇಉظॲཧʹൺ΂ͯഒҎ্ͷύ
ϑΥʔϚϯεΛୟ͖ग़͍ͯ͠Δɻແ৚݅ʹ͢΂ͯ
ͷ$BMMCBDLΛ๾໓ͯ͠͸͍͚ͳ͍ɻ
ϕϯνϚʔΫͷৄࡉ͸ԼهϦϙδτϦʹ
IUUQTHJUIVCDPN"KJEPXIJDIJTUIF
GBTUFTUBTZODQBUUFSO

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BTZODBXBJU͸1SPNJTFΑΓ΋଎͘ͳΔ
࠷৽ͷ؀ڥͰ֤ඇಉظॲཧͷύϑΥʔϚϯεΛܭଌɻ7Ҏ্Ͱ͸BXBJUͷ࢓༷ม
ߋΛ൐͏࠷దԽ͕ߦΘΕɺBTZODBXBJU͸1SPNJTFΑΓ΋ߴ଎ʹɻ
/PEFWʹೖΔ͔΋ɻ
Ϟδϡʔϧͷ಺෦Ͱ΋BTZODBXBJUΛར༻͠
ͯ1SPNJTFͷΠϯλʔϑΣʔεΛ࣮૷͢Δͱ͍
͏ํ๏͕ΑΓ༗ޮʹͳΔɻ
ͦͷ৔߹ɺࠓ೥݄ʹ&0-ͱͳΔ/PEFW؀
ڥΛߟྀ͢Δ͔Ͳ͏͔͕য఺ʹɻ
IUUQTWEFWCMPHGBTUBTZOD

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/PEFKTͷόʔδϣϯ͝ͱʹBTZODBXBJUͷύϑΥʔϚϯεΛܭଌ
‎BTZODBXBJU͸/PEFKTͷόʔδϣϯΞοϓʹ൐͍ܶతʹ଎౓͕޲্͍ͯ͠Δ
࠷దԽʹΑΓͦͷ଎౓͸$BMMCBDLʹഭΓ
ͭͭ͋Δɻ
1SPNJTFΑΓ΋BTZODBXBJUΛɻͦ͠
ͯBTZODBXBJUΛ׆༻͢ΔͳΒɺϥϯλ
ΠϜͷϝδϟʔόʔδϣϯΞοϓ͸ੵۃత
ʹߦͳ͍͖͍ͬͯͨɻ

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ετϦʔϜରԠ
4USFBNΛϑϩʔ੍ޚʹͲ͏૊ΈࠐΉʁ

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4USFBNͱϑϩʔ੍ޚ͸૬ੑ͕ѱ͍
͜Ε·Ͱ4USFBNΛϑϩʔ੍ޚʹ૊ΈࠐΉ৔߹͸ɺ1SPNJTF
ͰแΈࠐΈϫϯγϣοτͷΠϯλʔϑΣʔεʹม׵͢Δ͔ɺ
ಠࣗʹΠςϨʔγϣϯରԠͤ͞Δͱ͍͏ঢ়گͩͬͨɻ
const recv = new Promise((resolve, reject) => {
let data = ''
stream.on('data', (chunk) => {
data += chunk
})
stream.once('end', () => {
return resolve(data)
})
stream.once(‘error', (err) => {
return reject(err)
})
})
const data = await recv()
const drain = (stream) => {
return new Promise((resolve, reject) => {
stream.once('data', (data) => {
stream.pause()
…
resolve(data)
})
stream.once('end', () => {
…
resolve(null)
})
stream.once('error', (err) => {
…
reject(err)
})
stream.resume()
})
}
const main = async () => {
const stream = fs.createReadStream(‘file’)
let data = null
while (data = await drain(stream)) {
console.log(data)
}
}
1SPNJTFͰแΈࠐΉ
ϫϯγϣοτม׵
ෳࡶ೉ղͳ
ΠςϨʔγϣϯରԠ

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4USFBNͷΤϥʔϋϯυϦϯά͸ಠಛ
4USFBNͷجఈΫϥεͰ͋Δ&WFOU&NJUUFSͷΤϥʔϋϯυϦϯά͸ಠಛͰ͋Γɺͦ
ͷϋϯυϦϯά࿙Ε͸ϓϩηεͷΫϥογϡʹ௚݁͢Δɻಛʹ஫ҙ͕ඞཁͳઃܭύλʔ
ϯͷͻͱͭɻ
ઃܭύλʔϯ ΤϥʔϋϯυϦϯά Ϋϥογϡ
ඇಉظॲཧ
$BMMCBDL if (err)
&WFOU&NJUUFS emitter.on(‘error')
1SPNJTF .catch()
BTZODBXBJU try..catch .catch()
ಉظॲཧ try..catch 1SPNJTFBTZODBXBJU

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"TZOD*UFSBUPSΛ࢖ͬͨ4USFBNͷϑϩʔ੍ޚ
stream.on('data', (data) => {
console.log(data)
})
stream.on('end', () => {
console.log('finished')
})
stream.on(‘error', (err) => {
console.error(err)
})
try {
for await (const data of stream) {
console.log(data)
}
console.log(‘finished')
} catch (err) {
console.error(err)
}
4USFBN "TZOD*UFSBUPS
&4ͷػೳ"TZOD*UFSBUPSΛ׆༻͢Δ͜ͱͰɺ4USFBNΛγʔϜϨεʹϑϩʔ
੍ޚʹ૊ΈࠐΉ͜ͱ͕Ͱ͖ΔΑ͏ʹͳͬͨɻʢ&YQFSJNFOUBM"1*/PEFWʣ

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"TZOD*UFSBUPSΛ࢖ͬͨ4USFBNͷϑϩʔ੍ޚ
ςΩετϑΝΠϧΛߦ୯ҐͰॲཧͨ͠Γɺ)551ϦΫΤετͷDIVOLΛॲཧ͢Δ৔໘ͳ
ͲͰ׆༻Ͱ͖Δɻ౷ҰతͳΤϥʔϋϯυϦϯά͕ඇৗʹັྗతɻ
http.createServer(async (req, res) => {
try {
let body = ''
req.setEncoding('utf8')
for await (const chunk of req) {
body += chunk
}
console.log(body)
res.end()
} catch {
res.statusCode = 500
res.end()
}
})
const rl = readline.createInterface({
input: fs.createReadStream('input.txt')
})
for await (const line of rl) {
console.log(line)
}
}
main().catch((err) => {
console.error(err)
})
࣍ʹ๾໓͞ΕΔͷ͸4USFBN͔ʁ

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Τϥʔॲཧ
ඇಉظॲཧͷελοΫτϨʔε͸Ͳ͏ݟ͑Δʁ

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ඇಉظॲཧ๊͕͑ΔελοΫτϨʔεͷ՝୊ʢʣ
ຊདྷελοΫτϨʔε͸σόοάͷॿ͚ʹͳΔ΋ͷ͕ͩɺඇಉظॲཧͷελοΫτϨʔ
ε͸໾ʹཱͨͳ͍ɻඇಉظॲཧͷݺͼग़͠ݩ͸ɺඇಉظॲཧͷ։࢝Λ໋ྩͨ͠ίʔυͰ
͸ͳ͘ΠϕϯτϧʔϓͰ͋ΔͨΊɺಠཱͨ͠ελοΫτϨʔε͕දࣔ͞Εͯ͠·͏ɻ
const exec = require('child_process').exec
const func = (cb) => {
exec('exit 1', (err) => {
cb(err)
})
}
func((err) => {
console.error(err)
})
Error: Command failed: exit 1
at ChildProcess.exithandler
at ChildProcess.emit
at maybeClose
at Socket.stream.socket.on
at Socket.emit
at Pipe._handle.close
࣮ߦ݁Ռ
ݺͼग़͠ݩͷGVODؚ͕·Ε͓ͯΒͣ
ΤϥʔͷൃੜՕॴ͕ಛఆͰ͖ͳ͍

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ඇಉظॲཧ๊͕͑ΔελοΫτϨʔεͷ՝୊ʢʣ
"TZOD'VODUJPOͷ؀ڥԼͰ͸BXBJUʹΑͬͯελοΫτϨʔε͕෼཭͞ΕΔɻBXBJU
Ͱதஅ͞Εͨؔ਺͸ϚΠΫϩλεΫΩϡʔ͔Βॲཧ͕࠶։͞ΕΔͨΊɺલड़ͷ໰୊ͱಉ
༷ʹؔ਺ͷݺͼग़͠ܦ࿏͕ҡ࣋͞Εͣɺ੾Γ཭͞Εͯ͠·͏ɻ
const func = async () => {
await 'interrupt'
throw new Error('error')
}
await func()
}
console.error(err)
})
Error: error
at func
at process._tickCallback
at Function.Module.runMain
at startup
at bootstrapNodeJSCore
࣮ߦ݁Ռ
ݺͼग़͠ݩͷNBJOؚ͕·Ε͓ͯΒͣ
ΤϥʔͷൃੜՕॴ͕ಛఆͰ͖ͳ͍

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ඇಉظॲཧ๊͕͑ΔελοΫτϨʔεͷ՝୊ʹରॲ͢Δ
લड़ͨ͠ελοΫτϨʔεͷ՝୊͸ҎԼʹྻڍͨ͠ํ๏ʹΑͬͯରॲͰ͖Δɻ
ํ๏ ֓ཁ
JOTQFDUCSL$ISPNF%FW5PPMT
w ༷ʑͳσόοάػೳΛ಺แ
w Φʔόʔϔου͋Γʢߴίετʣ
BTZOD@IPPLTUSBDFDMBSJGZ
w ߴ͍Մಡੑͱ࢖͍উखͷྑ͞
w Φʔόʔϔου͋Γ
BTZODTUBDLUSBDFT
w Φʔόʔϔουͳ͠
w BTZODBXBJUͷ՝୊ͷΈղܾՄೳ

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JOTQFDUCSL$ISPNF%FW5PPMT
JOTQFDUCSLΦϓγϣ
ϯ෇͖Ͱىಈɻ
$ISPNF%FW5PPMT͔
Β֬ೝ͢Δɻ
ελοΫτϨʔεʹ͸දࣔ͞Εͳ͍
ܦ࿏΋දࣔ͞ΕΔ

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BTZOD@IPPLTUSBDFDMBSJGZ
USBDFϞδϡʔϧ͸ඪ४ϞδϡʔϧͷBTZOD@IPPLTΛར༻ͯ͠ɺඇಉظॲཧʹಠࣗίʔ
υΛࠩ͠ࠐΈελοΫτϨʔεΛ֦ு͢ΔɻDMBSJGZϞδϡʔϧ͸ෆཁͳελοΫτϨʔ
εΛআڈͯ͠ελοΫτϨʔεͷՄಡੑΛ޲্ͤ͞Δɻʢݸਓత͓͢͢Ίʣ
❯ node -r trace -r clarify exec.js
Error: Command failed: exit 1
at func
at Object.
࣮ߦ݁Ռ
ݺͼग़͠ݩͷGVODؚ͕·Ε
ෆཁͳߦ΋࡟আ͞Ε͍ͯΔ
const exec = require('child_process').exec
const func = (cb) => {
exec('exit 1', (err) => {
cb(err)
})
}
func((err) => {
console.error(err)
})

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BTZODTUBDLUSBDFT
7Ҏ্ͷ؀ڥͰ͜ͷΦϓγϣϯΛ༗ޮʹ͢ΔͱɺBXBJUʹؚ·ΕΔ৘ใΛ࢖ͬͯ
ඇಉظॲཧΛލ͍ͩελοΫτϨʔε͕ߏங͞ΕΔΑ͏ʹͳΔɻ෦෼తͳ໰୊ղܾखஈ
Ͱ͸͋Δ͕ɺ࣮ߦதͷγεςϜʹෛՙΛ༩͑ͳֵ͍৽తͳػೳɻ
const func = async () => {
await 'interrupt'
throw new Error('error')
}
await func()
}
console.error(err)
})
❯ node --async-stack-traces await.js
Error: error
at func
at process._tickCallback
at Function.Module.runMain
at startup
at bootstrapNodeJSCore
at async main
࣮ߦ݁Ռ
ݺͼग़͠ݩͷNBJOؚ͕·Ε͍ͯΔ
·ͩϑϥά෇͖ͷػೳɻࠓޙͷϑϥάղআʹظ଴

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ϑϩʔ੍ޚͷ࠷దԽ͸$BMMCBDLΛ1SPNJTFʹม͚͑ͨͩͰ͸
ऴΘΒͳ͍ɻকདྷΛݟਾ͑ɺ͞ΒͳΔ࠷దԽΛਐΊΑ͏ʂ
‣ BTZODBXBJU͸վྑ͞Εɺߴ଎Խ͠ଓ͚͍ͯΔ
‣ 1SPNJTFΑΓ΋BTZODBXBJUͷੵۃతͳ׆༻Λ
‣ 4USFBNͷϑϩʔ੍ޚʹର͢Δ࠷దԽ͸ؒۙ
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Callback to Promise and beyond

Callback to Promise and beyond

Daiki Kuriyama

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