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async 完全理解 - 全ての async は Promise に通ず / Guide to...
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saiya_moebius
December 04, 2020
Programming
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async 完全理解 - 全ての async は Promise に通ず / Guide to async, await
saiya_moebius
December 04, 2020
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Transcript
None
None
None
Promise Deferred Objects async await Promise async await
None
Promise<T> ( ) ( ) resolve(T) Promise reject(any) Promise then(f,
f) , ,
Promise<T> ( ) ( ) resolve(T) Promise reject(any) Promise then(f,
f) , ,
async return throw await const value = await ; console.debug(value);
.then((value) => { console.debug(value); });
None
None
None
const promise = new Promise(); // ... ... promise.resolve( );
/* */ promise.reject( ); new Promise((resolve, reject) => { // ... ... resolve( ); /* */ reject( ); });
// Promise let resolve, reject; new Promise((_resolve, _reject) => {
// resolve, reject resolve = _resolve; reject = _reject; }); resolve( ); /* */ reject( ); // ↑ ...
function () { // Promise ... const promise = new
Promise(); // ... ( promise.resolve ) ... return promise; } const promise = (); promise.resolve(null); // resolve
function () { // Promise return new Promise((resolve, reject) =>
{ // ... ( resolve ) ... }); } const promise = (); // ↑ resolve
function (props) { // const hoge = props.something.foobar(); // Promise
... const promise = new Promise(); // ... ( promise.resolve ) ... return promise; } resolve( ) reject( )
None
function () { /* ※1 */ return new Promise((resolve, reject)
=> { // reject( ) }); } const promise = (); // ↑ Promise reject ※1
promise.then .then((result) => { return (); // Promise }).then((result) =>
{ // result === });
Promise.all(Promise<T>[]): Promise<T[]> Promise.race(Promise<T>[]): Promise<T> promise.catch(f)
function myFunction() { A().then((resultA) => { if (resultA === "hoge")
{ B().then((resultB) => { if (resultB === "huga") C(); }); } else { D().then((resultC) => { if (resultC === "piyo") E(); }); } }); }
None
None
async return throw await const value = await ; console.debug(value);
.then((value) => { console.debug(value); });
await // async function myFunction() { if (await A() ===
"hoge") { if (await B() === "huga") C(); } else { if (await D() === "piyo") E(); } } await then
None
Promise Promise.all Promise.race await Promise.all( 1(), 2(), ...) Promise
async await async Promise Promise await await
None
None
async await function hoge() { const async = 1; const
await = 2; console.log(async, await); // it works } async await async function() { ... } async
await async function myFunction() { await 1(); // 1().then(...) 1();
2(); // await 2(); await 3(); // 3().then(...) } 2 no-floating-promises
await Promise.resolve(Promise.resolve(123)); // Promise.resolve(123) 123 // Promise.resolve Promise
fulfill reject resolve Promise.reject(e) Promise.resolve(value) fulfill resolve reject
new Promise Promise. Promise
Promise Promise Promise = undefined; // Promise.resolve(1234); // await (async()
=> 123)(); // async await Promise Promise ZoneAwarePromise Promise Zone async await Promise.
await then await 14.6.13 Runtime Semantics: Evaluation 25.5.5.3 AsyncFunctionAwait (
value ) 25.4.5.3.1 PerformPromiseThen
await