I recently got me a membership of egghead.io (this is a referral code) to learn more about web development and all those new technologies. I watched a quick course about async / await and did some notes. These are the ones about sending parallel promises and awaiting them afterwards.
Sending multiple promises at the same time
async displayDevicesAndUsers() => {
// Since both promises are stored in variables,
// they are fetched in parallel from the api
const devicesPromise = fetchApi("devices");
const usersPromise = fetchApi("users");
// The results can then be extracted with await
const devices = await devicesPromise;
const user = await userPromise;
}
Promise.all
There is also an easier method. You can use Promise.all
. This will create one promise, that will reserve when all promises in itβs array resolved. The promise will be rejected when one of the promises inside fails. I will use the previous example and refactor it with Promise.all
async displayDevicesAndUsers() => {
// 1st option to retrieve results
const results = Promise.all([
fetchApi("devices");
fetchApi("users");
]);
const devices = results[0];
const users = results[1];
// 2nd option, which is a little shorter
// and uses ES2015 array destructuring
const [devices, users] = Promise.all([
fetchFromGitHub("devices");
fetchFromGitHub("users");
]);
}
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