Is there any difference between:
const [result1, result2] = await Promise.all([task1(), task2()]);
and
const t1 = task1();
const t2 = task2();
const result1 = await t1;
const result2 = await t2;
and
const [t1, t2] = [task1(), task2()];
const [result1, result2] = [await t1, await t2];
Generally, using Promise.all() runs requests "async" in parallel. Using await can run in parallel OR be "sync" blocking.
test1 and test2 functions below show how await can run async or sync.
test3 shows Promise.all() that is async.
jsfiddle with timed results - open browser console to see test results
Sync behavior. Does NOT run in parallel, takes ~1800ms:
const test1 = async () => {
const delay1 = await Promise.delay(600); //runs 1st
const delay2 = await Promise.delay(600); //waits 600 for delay1 to run
const delay3 = await Promise.delay(600); //waits 600 more for delay2 to run
};
Async behavior. Runs in paralel, takes ~600ms:
const test2 = async () => {
const delay1 = Promise.delay(600);
const delay2 = Promise.delay(600);
const delay3 = Promise.delay(600);
const data1 = await delay1;
const data2 = await delay2;
const data3 = await delay3; //runs all delays simultaneously
}
Async behavior. Runs in parallel, takes ~600ms:
const test3 = async () => {
await Promise.all([
Promise.delay(600),
Promise.delay(600),
Promise.delay(600)]); //runs all delays simultaneously
};
TLDR; If you are using Promise.all() it will also "fast-fail" - stop running at the time of the first failure of any of the included functions.