快速构建Promise.all（）的承诺数组

Question

so I've been trying to use the Promise.all() method and I'm running into an issue where I need to pass the method an array of promises, but I'm not sure how many promises are going to be called for/needed by the application.

Here's a method that I've gotten working by specifically building the array

router.post('/test1', (req, res, next) => {
    console.log('Hit on POST /test1');
    let arr = ['email1@email.com','email2@email.com'];
    Promise.all([
      lookUpUserId(arr[0]),
      lookUpUserId(arr[1])
    ]).then((x)=>{res.send(x)});
});

My lookUpUserId() function is returning a promise and I'm able to use it if I explicitly list them in the array. However I've tried a few methods of creating this array on the fly and I can't seem to get it working.
Example #1

router.post('/test1', (req,res,next) => {
    console.log('Hit on POST /test1');
    let arr = ['email1@email.com','email2@email.com'];
    Promise.all((arr)=>{
      let out = [];
      for(let i=0; i<arr.length; i++){
        out.push(lookUpUserId(arr[i]));
      }
      return out;
    }).then((x)=>{res.send(x)});
});

Example 2

outer.post('/test1', (req,res,next) => {
    console.log('Hit on POST /test1');
    let arr = ['email1@email.com','email2@email.com'];
    let promArr = (arr)=>{
      let out = [];
      for(let i=0; i<arr.length; i++){
        out.push(lookUpUserId(arr[i]));
      }
    }
    Promise.all(promArr).then((x)=>{res.send(x)});
});

Answer 1

You can use Array.prototype.map() where the first parameter to lookUpUserId function is expected to be an element of arr

router.post('/test1', (req, res, next) => {
    console.log('Hit on POST /test1');
    let arr = ['email1@email.com','email2@email.com'];
    Promise.all(arr.map(lookUpUserId))
    .then(x => res.send(x));
});

The issue with second approach is that you do not call the function, pass the array as parameter to the function, or return the out array from the function

outer.post('/test1', (req,res,next) => {
    console.log('Hit on POST /test1');
    let arr = ['email1@email.com','email2@email.com'];
    let promArr = arr => {
      let out = [];
      for(let i=0; i<arr.length; i++) {
        out.push(lookUpUserId(arr[i]));
      }
      return out // `return` the array of `Promise` objects
    }
    Promise.all(promArr(arr)).then(x => res.send(x));
});

Answer 2

It's the same problem in both scenarios....your not actually invoking the function call therefore you never pass the array to Promise.all.

Using the second example, purely because it's easier to demonstrate the fix, try:

Promise.all(promAll(arr))
    .then(...)
    .catch(...)