use promise in javascript reduce() code example
Example: es6 reduce return promise
async function slowCounter () {
const ret = await ([100, 200, 300, 400, 500]).reduce(
async (promise, wait, idx) => {
return promise.then(async last => {
const ret = last + wait
console.log(`${idx}: waiting ${wait}ms to return ${ret}`)
await new Promise((res, rej) => setTimeout(res, wait))
return ret
})
}, Promise.resolve(0))
console.log(ret)
}
slowCounter ()