如何解决 promise 在 map 链中制作 function 的问题？

Question

I'd like all the slowAdd()s in the code below to happen in parallel, but I don't want to do the next.map() step until they are all resolved. How to do it?

async function slowAdd(a) {
  return new Promise( (resolve,reject) => setTimeout(() => resolve(a+5), 1000) )
}

async function calcArray(list) {
  return list
    .map( a => a+1 )
    .map( a => slowAdd(a) )
    .map( a => a+1 )
}

async function main() {
  const list = [1, 2, 3, 4, 5]
  const newList = await calcArray(list)
  console.log(newList)
}

main()
  .catch(err => {
    console.error(err);
  })
  .then(() => process.exit());

Answer 1

Put it in a Promise.all , and then you'll need another .map inside a .then for the subsequent action:

 async function slowAdd(a) { return new Promise( (resolve,reject) => setTimeout(() => resolve(a+5), 1000) ) } async function calcArray(list) { return Promise.all( list.map( a => a+1 ).map( a => slowAdd(a) ) ).then(addedResults => addedResults.map( a => a+1 )); } async function main() { const list = [1, 2, 3, 4, 5] const newList = await calcArray(list) console.log(newList) } main()