Promise.all là gì?
Promise.all là gì? Hiểu và sử dụng promise all trong những trường hợp nào trong vòng 1 phút.
// setup
const wait = value => new Promise(resolve => {
setTimeout(() => resolve(value), 3000);
});
const fetchFoo = () => wait('foo');
const fetchBar = () => wait('bar');
const fetchBaz = () => wait('baz');
const fetchDataSlowly = async time => {
// Bad. Requests run in serial waterfall.
const foo = await fetchFoo();
const bar = await fetchBar();
const baz = await fetchBaz();
return { foo, bar, baz, time: Date.now() - time };
};
fetchDataSlowly(Date.now())
.then(({ foo, bar, baz, time }) => {
console.log('fetched slowly:', foo, bar, baz, time
);
});
const fetchDataQuickly = async time => {
// Good. Fetches run in parallel.
const [
foo,
bar,
baz
] = await Promise.all([
fetchFoo(),
fetchBar(),
fetchBaz()
]);
return { foo, bar, baz, time: Date.now() - time };
};
fetchDataQuickly(Date.now())
.then(({ foo, bar, baz, time}) => {
console.log('fetched quickly:', foo, bar, baz, time);
});
const fetchDataQuickly2 = async time => {
// Also good.
const fooReady = fetchFoo();
const barReady = fetchBar();
const bazReady = fetchBaz();
const foo = await fooReady;
const bar = await barReady;
const baz = await bazReady;
return { foo, bar, baz, time: Date.now() - time };
};
fetchDataQuickly2(Date.now())
.then(({ foo, bar, baz, time}) => {
console.log('fetched quickly:', foo, bar, baz, time);
});Có thể bạn đã miss một số snippets code