03. Await Expression

Если в асинхронной функции встречается выражение с ключевым словом await, значением которого является Promise, то она приостанавливает свою работу (как генератор) до тех пор, пока Promise не будет установлен:

• If the Promise is fulfilled, the result of await is the fulfillment value.

• If the Promise is rejected, await throws the rejection value.

Every await expression suspend execution. A function with multiple await expressions in it will be suspended once at a time on each await expression until that Promise is settled, before unsuspending execution and moving onto the next await expression

Handling a single asynchronous result

async function asyncFunc() {
  const result = await otherAsyncFunc();
  console.log(result);
}

// Equivalent to:
function asyncFunc() {
  return otherAsyncFunc().then(result => {
    console.log(result);
  });
}

Detach promise from await

Можно отделять вызов async операции от await результата на ней:

async function asyncFunc() {
  const promise = otherAsyncFunc();
  const result = await promise;
  console.log(result);
}

Handling multiple asynchronous results in parallel

Note that await is sequential, Promise.all() is parallel:

async function asyncFunc() {
    const [result1, result2] = await Promise.all([
        otherAsyncFunc1(),
        otherAsyncFunc2(),
    ]);
    console.log(result1, result2);
}

// Equivalent to:
function asyncFunc() {
    return Promise.all([
        otherAsyncFunc1(),
        otherAsyncFunc2(),
    ])
    .then([result1, result2] => {
        console.log(result1, result2);
    });
}