Summary - If the mapping function is asynchronous:
To make asyncIter continue producing values without waiting for each mapping to finish, use
async function asyncIterMap(asyncIter, asyncFunc) {
const promises = [];
for await (const value of asyncIter) {
promises.push(asyncFunc(value))
}
return await Promise.all(promises)
}
// example - how to implement:
const results = await asyncIterMap(myAsyncIter(), async (str) => {
await sleep(3000)
return str.toUpperCase()
});
Further Explanation:
// mock asyncIterator for illustration purposes
const sleep = (ms) => new Promise(res => setTimeout(res, ms))
async function* myAsyncIter() {
await sleep(1000)
yield 'first thing'
await sleep(1000)
yield 'second thing'
await sleep(1000)
yield 'third thing'
}
Next
// THE CURRENT SCENARIO! our asyncIter waits for each mapping.
for await (const thing of myAsyncIter()) {
console.log('beginning with', thing)
await sleep(3000)
console.log('concluded with', thing)
}
// complete execution time: ~12 seconds
Improved version:
// this is a better approach.
const promises = [];
for await (const thing of myAsyncIter()) {
const task = async () => {
console.log('commencing with', thing)
await sleep(3000)
console.log('finished with', thing)
};
promises.push(task())
}
await Promise.all(promises)
// total run time: ~6 seconds