How Async Await behaves in loops
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// our cool promise of future; serialize promises | |
function future(val){ | |
console.log("lala ", val); | |
return new Promise((resolve, reject) => { | |
setTimeout(resolve, 2000, val); | |
}) | |
} | |
//1. await waits in this case | |
(async () => { | |
for (i in [1,2,3,4]) { | |
const x = await future(i); | |
console.log(x) | |
} | |
console.log('done') | |
})() | |
/* | |
lala 0 | |
Promise {<pending>} | |
0 | |
lala 1 | |
1 | |
lala 2 | |
2 | |
lala 3 | |
3 | |
done | |
*/ | |
//2. await won't wait in this case; fire and forget | |
(() => { | |
[1,2,3,4].forEach(async i => { | |
let x = await future(i); | |
console.log('-> ', x) | |
}); | |
console.log("done") | |
})() | |
/* | |
lala 1 | |
lala 2 | |
lala 3 | |
lala 4 | |
done | |
undefined | |
-> 1 | |
-> 2 | |
-> 3 | |
-> 4 | |
*/ | |
// 3.make use of inherent parallelism | |
(() => { | |
Promise.all([1,2,3,4].map(i => future(i))) | |
.then(result => result.forEach(x => console.log('-> ', x))); | |
console.log("done") | |
})() | |
/* | |
lala 1 | |
lala 2 | |
lala 3 | |
lala 4 | |
done | |
undefined | |
-> 1 | |
-> 2 | |
-> 3 | |
-> 4 | |
*/ |
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